3rd Nephi 15-23:
And they understood me not that I said they shall hear my voice; and they understood me not that the Gentiles should not at any time hear my voice—that I should not manifest myself unto them save it were by the Holy Ghost.
Would this not pertain to Joseph Smith also, being that he was a gentile? Doesn’t this go against the story of the appearance of the Father and Son to Joseph Smith?
Where did you get the idea that Joseph Smith was a gentile? The prophet Joseph was of the house of Israel and was a descendant of Ephraim. Here are the words of Eldred G. Smith, the patriarch to the Mormon Church on the matter—
“Jacob blessed his twelve sons and gave them each a blessing suited to their individual rewards and pronounced promises that should come to them. Joseph received a special blessing which we are most interested in because we are his descendants, the most part of us, and the blessings of the gospel have come through this line, for Joseph Smith, Senior, was a true descendant, through Ephraim, the younger son of Joseph” (Elder Eldred G. Smith, Conference Report, April 1952).