When Jacob was still young, he received his calling directly from the Lord. Lehi explained that Joseph had seen the Lord, thou hast beheld in thy youth his glory (2 Nephi 2:4). This is a good example of a prophet who received his calling directly from the Lord, And no man taketh this honour unto himself, but he that is called of God, as was Aaron (Heb 5:4). Because of his righteousness, he was ordained after the manner of his holy order.
The phrase "his holy order" is reminiscent of the full name of the Melchizedek priesthood, or the Holy Priesthood after the Order of the Son of God (DC 107:3). This was the priesthood held by the Nephites. Although there were descendants of Manasseh (Lehi), Ephraim (Ishmael), and Judah (Mulek) among the Nephites, there was not any of the blood of Levi. Therefore, they did not hold the Levitical or Aaronic priesthood.
"It should be noted that those consecrated priests and teachers among the Nephites were not receiving offices in the lesser priesthood, for there was no Aaronic Priesthood among the Nephites from the time Lehi left Jerusalem down to the ministry of Christ among them." (Mormon Doctrine, 776)