Thus they become high priests forever, after the order of the Son, the Only Begotten of the Father, who is without beginning of days or end of years, who is full of grace, equity, and truth. And thus it is. Amen. (Alma 13:9, just one of many texts in uniquely LDS Scripture teaching the eternal existence of Jesus)
It is a common objection that Latter-day Saint Christology is “Arian.” However, such a claim is simply false. For an article addressing this, see:
Alexander Campbell in his review of the Book of Mormon, "Delusions" from the Millennial Harbinger 2, no. 2 (7 February, 1831) wrote the following:
Mormon was very orthodox, for he preached in these words, A.D. 362: - 'That Jesus was the very Christ and the very God.' He must have heard of the Arian controversy by some angel!!
In spite of being a vehement critic of Joseph Smith and the Book of Mormon, Campbell did realise that neither preached an Arian Christology. Commenting on the above criticism from Campbell of the high Christology in the Book of Mormon, RoseAnn Benson wrote:
Campbell was correct in stating that neither the prophet Mormon nor Joseph Smith taught Arianism. Jesus Christ is subordinated to his Father, but not because of the statements of the Nicene Creed. Smith taught that “Christ came according to the words of John, & he was greater than John because he held the keys of the Melchesedic Priesthood & the kingdom of God & had before revealed the priesthood to Moses. Yet Christ was baptized by John to fulfill all righteousness.” Joseph Smith, 22 January 1843, in Wilford Woodruff’s Journal, 2:216. In other words, the premortal Christ had priesthood authority and appeared to Moses and other Old Testament and Book of Mormon prophets for the purpose of dispensing that power. He is the Father of heaven and earth, and the Creator of all things from the beginning and is the God who condescended to come to earth to redeem his people. He has always been a member of the Godhead, but subordinate to his Father as his Son, to whom he obeyed, praised, and prayed. (RoseAnn Benson, Alexander Campbell and Joseph Smith: 19th-Century Restorationists [Provo: Brigham Young University Press, 2017], 269 n. 28)
To be fair, even modern critics of the LDS Church and its Christology will readily admit that "Mormon" Christology is not "Arian." As one critic of the Church wrote once in response to a fellow Evangelical who falsely stated Mormonism teaches Jesus is "created":
