Plutarch explains how Isis searches for body parts of Osiris.
Plutarch, Isis and Osiris, trans. Frank Cole Babbitt (Cambridge: Loeb Classical Library, 1936), 44-47
The traditional result of Osiris's dismemberment is that there are many so‑called tombs of Osiris in Egypt; for Isis held a funeral for each part when she had found it. Others deny this and assert that she caused effigies of him to be made and these she distributed among the several cities, pretending that she was giving them his body, in order that he might receive divine honours in a greater number of cities, Band also that, if Typhon should succeed in overpowering Horus, he might despair of ever finding the true tomb when so many were pointed out to him, all of them called the tomb of Osiris.
Of the parts of Osiris's body the only one which Isis did not find was the male member, for the reason that this had been at once tossed into the river, and the lepidotus, the sea-bream, and the pike had fed upon it; and it is from these very fishes the Egyptians are most scrupulous in abstaining. But Isis made a replica of the member to take its place, and consecrated the phallus, in honour of which the Egyptians even at the present day celebrate a festival.