The Lds Prophet Joseph Smith wrote, "We believe in God, the eternal Father, and in His Son, Jesus Christ, and in the Holy Ghost."

Doctrine & Covenants 93:30 teaches us...

All truth is independent in that sphere in which God has placed it, to act for itself, as all intelligence also; otherwise there is no existence.

"Eternal" and all other words of scripture, are defined to apply within this Plan of Salvation — a plan that started with the spiritual creation of Jesus Christ and will end at the end of the Millenial reign of Jesus Christ with the final judgement and exaltation of the Earth. There is very little revealed about what happened before that beginning or after that end.

But, what is time to a God? We do not believe in "creating God in Man's image." One of the best examples of this problem are the numerologists' efforts to treat the 1,000 years-to-a-day equation found in several scriptural locations as literal when, in reality, it's God's best effort to explain the concept of timelessness to mortals who are fixated on the concept of time. This idea is used in Alma 13:7:

This high priesthood being after the order of his Son, which order was from the foundation of the world; or in other words, being without beginning of days or end of years, being prepared from eternity to all eternity.

And yet there was a proverbial "moment in time" (if we once again create God in our own image) when the world was founded. This concept of "eternity" being bracketed by a beginning is not unique to the LDS Church. It can also be seen in Proverbs 8:23.

I was set up from everlasting, from the beginning, or ever the earth was.

Indeed, in at least one instance, the word "eternal" is not used in the Bible to mean "all time past and future." In 2 Corinthians 4:18 we read:

While we look not at the things which are seen, but at the things which are not seen: for the things which are seen are temporal; but the things which are not seen are eternal.

Where the word "eternal" mirrors the word "temporal." "Eternal" is, apparently, a legitimate synonym for "spiritual" or "Godly." Or, from the LDS perspective, "something that doesn't live briefly and die."

Joseph Smith did not contradict himself using the word "eternal." From the LDS perspective, the word means, "always within this Plan." It's the the world that has imposed the false concept of "all time past and future" onto the word "eternal."

He also does not contradict himself with the word "immortal," either. It's a much longer discussion (one that I'm pretty sure already exists as an answer on this site), but in a nutshell: Judgment leads to resurrection which is thereafter, immortal. Though we have few teachings that extend beyond the scope of this Plan of Salvation, Church dogma is that once raised from corruption to incorruption, the body (and the being) are immortal, timeless and undestroyable (aka "without death" or an end). So, once again, no discrepancy.

At least, not from our perspective.

This is how Joseph Smith argued it in that sermon:

We have imagined that God was God from all eternity. These are incomprehensible ideas to some, but they are the simple and first principles of the gospel, to know for a certainty the character of God, that we may converse with him as one man with another, and that God himself; the Father of us all dwelt on an earth the same as Jesus Christ himself did, and I will show it from the Bible. I wish I had the trump of an arch angel, I could tell the story in such a manner that persecution would cease forever; what did Jesus say? (mark it elder [Sidney] Rigdon;) Jesus said, as the Father hath power in himself, even so hath the Son power; to do what? why what the Father did, that answer is obvious; in a manner to lay down his body and take it up again. Jesus what are you going to do? To lay down my life, as my Father did, and take it up again.— If you do not believe it, you do not believe the Bible

"Discourse, 7 April 1844, as Reported by Times and Seasons," p. 614, The Joseph Smith Papers, accessed July 5, 2020, https://www.josephsmithpapers.org/paper-summary/discourse-7-april-1844-as-reported-by-times-and-seasons/3

I think the scripture in mind is probably John 5:19

Then answered Jesus and said unto them, Verily, verily, I say unto you, The Son can do nothing of himself, but what he seeth the Father do: for what things soever he doeth, these also doeth the Son likewise.

or John 5:26

For as the Father hath life in himself; so hath he given to the Son to have life in himself;

Introduction: Let’s start with a brief overview to establish who’s who from the LDS point of view:

Latter-day Saints commonly refer to God the Eternal Father as Elohim, a Hebrew plural meaning God or gods, and to his Son Jesus Christ, as Jehovah.

The first spirit son of Elohim (Heavenly Father) and his wife (Heavenly Mother) is called Jehovah.

Jehovah came to earth as Jesus to be born as a man in order to progress to godhood (exaltation).

To members of the Church of Jesus Christ of latter-day Saints there is no one else higher then Heavenly Father (Elohim).

God the Father is the Supreme Being. He is the ultimate Creator, Ruler, and Preserver of all things.

He is the God over all creation as Latter Day Saints know it. Take note of that statement. Hebrews 1:2 is used as evidence that there are many worlds. Elohim is God over this world.

Father in Heaven: The Father of the spirits of all mankind. Jesus is his Only Begotten Son in the flesh. Man has been commanded to obey and give reverence to the Father and to pray to him in Jesus’ name.

God the Son: The God known as Jehovah is the Son, Jesus Christ… he is the eldest of the spirit children of Elohim... it was actually Jesus who was the Creator under the direction of God the Father [Elohim].

Godhead: https://www.lds.org/scriptures/gs/god-godhead?lang=eng&letter=g

Jesus Christ: https://www.lds.org/scriptures/gs/jesus-christ?lang=eng

Jehovah: https://www.lds.org/scriptures/gs/jehovah?lang=eng&letter=j

Brief overview of LDS theology with regard to God the Father, Jesus Christ, the Son of God and the Eternal Father: About 124 B.C. the book of Mosiah (in the Book of Mormon) made these prophesies:

For behold, the time cometh, and is not far distant, that with power, the Lord Omnipotent who reigneth, who was, and is from all eternity to all eternity, shall come down from heaven among the children of men... And he shall be called Jesus Christ, the Son of God, the Father of heaven and earth, the Creator of all things from the beginning; and his mother shall be called Mary. (Mosiah 3:5 and 8)

Note that it is “the Lord Omnipotent” who is to come down from heaven to be called Jesus Christ. He is “the Son of God, the Father of heaven and earth, the Creator of all things from the beginning.” Mosiah chapter 15 goes on to say Father and Son are one God, the Eternal Father:

God himself shall come down among the children of men, and shall redeem his people. And because he dwelleth in flesh he shall be called the Son of God, and having subjected the flesh to the will of the Father, being the Father and the Son - the Father, because he was conceived by the power of God; and the Son, because of the flesh; thus becoming the Father and Son - And they are one God, yea, the very Eternal Father of heaven and of earth (Mosiah 15:1-4).

God the Eternal Father was once a mortal man who passed through a school of earth life similar to that through which we are now passing (The Gospel Through the Ages, 1945, p 104).

I am going to tell you how God came to be God. We have imagined and supposed that God was God from all eternity. I will refute that idea, and take away the veil, so that you may see. … It is the first principle of the Gospel to know for a certainty the character of God and to know...that he was once a man like us.... (“King Follett Discourse,” Journal of Discourses 6:3-4, also in Teachings of the Prophet Joseph Smith, 345-346, and History of the Church, vol. 6, 305-307) http://mit.irr.org/god-was-once-man-us-finessing-off-putting-mormon-doctrine

In the Bible Jesus says God is Spirit, and his worshippers must worship in spirit and in truth (John 4:24). However, Joseph Smith saw fit to change these words to deny that God (read Elohim) is Spirit:

Is God a spirit? John 2–4: “Ye Must Be Born Again” John 4:24: Some may be confused by Jesus’s statement that God is a spirit. The Joseph Smith Translation of this verse provides an important clarification: “For unto such hath God promised his Spirit” (in John 4:24, footnote a). Modern revelation also teaches that God has a body of flesh and bones (see D&C 130:22–23; see also Genesis 5:1–3; Hebrews 1:1–3). [1] https://www.churchofjesuschrist.org/study/manual/come-follow-me-for-individuals-and-families-new-testament-2019/07.scripture_title4-p11#scripture_title4

The manifestation of God's physical body came in a revelation to Joseph Smith in 1843:

The Father has a body of flesh and bones as tangible as man’s; the Son also; but the Holy Ghost has not a body of flesh and bones, but is a personage of Spirit. Were it not so, the Holy Ghost could not dwell in us. https://www.churchofjesuschrist.org/study/scriptures/dc-testament/dc/130.22?lang=eng#21

The Bible says that God is from everlasting to everlasting (Psalm 90:2) and that He is eternal (1 Timothy 1:17). He is the Alpha and the Omega, the First and the Last, the beginning and the end (Revelation 1:8; 21:6; 22:13). God the creator was not himself created. But the Book of Mormon says God was once a man and has a body of flesh and bones. Mormons worship Elohim, God the Father, through Jesus, God the Son. They are God the Eternal Father. What is unclear is who created the man who became God the Eternal Father. What is also unclear is whether Joseph Smith understood the difference in meaning between eternal and immortal. After all, how could a created being be eternal? Here is the LDS definition of ‘eternal life’ and ‘immortality’:

Eternal life is the phrase used in scripture to define the quality of life that our Eternal Father lives. The Lord declared, “This is my work and my glory—to bring to pass the immortality and eternal life of man” (Moses 1:39). Immortality is to live forever as a resurrected being. Source: https://www.churchofjesuschrist.org/study/manual/gospel-topics/eternal-life?lang=eng

Conclusion: One possible LDS justification or explanation for their belief that Elohim, the Supreme Being, also known as God the Eternal Father, or God the Father, or Heavenly Father, and who has a body of flesh and bones, is that Joseph Smith was the recipient of modern revelation [1]

Another is that the Book of Mormon trumps The Bible. [2]

Articles of Faith – 8: We believe the Bible to be the word of God as far as it is translated correctly; we also believe the Book of Mormon to be the word of God. [2] http://lds.org/scriptures/pgp?lang=eng

Disclaimer: In the Bible God the Father was never created, is not a man and He is not God the Son. And Jesus, the Son of God, is not Jehovah, nor is he God the Father. That’s what my Bible says, and I believe the Bible. If I have misrepresented the beliefs of the Church of Jesus Christ of Latter Day Saints I would appreciate an explanation of where I have gone wrong.