Nephi notes that he speaks:
concerning the prophecies of which my father hath spoken, concerning Joseph, who was carried into Egypt. For behold, he truly prophesied concerning all his seed. And the prophecies which he wrote, there are not many greater. And he prophesied concerning us, and our future generations; and they are written upon the plates of brass. (2 Nephi 4:1-2)
According to Daniel Ludlow, some of the writings of Joseph are still in existence but have not been published to the world in our present Bible. Joseph Smith said that he received some papyri scrolls that contained the record of Abraham and Joseph at the same time he obtained the Egyptian mummies from Michael Chandler. Concerning this record, Joseph Smith has written: "The record of Abraham and Joseph, found with the mummies, is beautifully written on papyrus, with black, and a small part red, ink or paint, in perfect preservation." (History of the Church, 2:348) The Prophet next describes how the mummies and the record came into his possession and then concludes: "Thus I have given a brief history of the manner in which the writings of the fathers, Abraham and Joseph, have been preserved, and how I came in possession of the same--a correct translation of which I shall give in its proper place." (History of the Church, 2:350-351).
The record of Abraham translated by the Prophet was subsequently printed, and it is now known as the book of Abraham in the Pearl of Great Price. However, the translation of the book of Joseph has not yet been published. Evidently the record of Joseph was translated by the Prophet, but perhaps the reason it was not published was because the great prophecies therein were "too great" for the people of this day. [Daniel H. Ludlow, A Companion to Your Study of the Book of Mormon, pp. 130-131]
Note* It should be remembered that some of Joseph's prophecies were restored to the Bible when Joseph Smith translated or revised it (see JST, Genesis 50:24-36). [Church Educational System, Book of Mormon Student Manual: Religion 121 and 122, 1989, p. 25]