The sons of Pharez were Hezron and Hamul - It is not likely that Pharez was more than ten years of age when he came into Egypt, and if so he could not have had children; therefore it is necessary to consider Hezron and Hamul as being born during the seventeen years that Jacob sojourned in Egypt, See Clarke on Genesis 46:8 (note): and it appears necessary, for several reasons, to take these seventeen years into the account, as it is very probable that what is called the going down into Egypt includes the seventeen years which Jacob spent there.

And the sons of Judah, Er, and Onan, and Shelah, and Pharez,

and Zarah,.... Five of them:

but Er and Onan died in the land of Canaan; and so did not go with Jacob into Egypt; and which is observed that they might not be reckoned among them, though it was proper to take notice of them in the genealogy:

and the sons of Pharez were Hezron and Hamul; some think that these could not be born in Canaan, but in Egypt; and that they are mentioned among those that went down to Egypt, because they went there in the loins of their father, and to supply the places of Er and Onan, who died before, and have the honour to be here named, because they might be the first of Jacob's great grandchildren born there; though others suppose that Pharez was at this time fourteen years of age, and instances are given of some, who before that age have been fathers of children; the difficulty is not easily solved: the Targum of Jonathan expressly says,"Shelah and Zarah did not beget children in Canaan, but there were two sons of Pharez who went down into Egypt, Hezron and Hamul.''

And the sons of Judah; Er, and Onan, and Shelah, and Pharez, and Zarah: but Er and Onan died in the land of Canaan. And the sons of Pharez were Hezron and Hamul.

46:5-27 We have here a particular account of Jacob's family. Though the fulfilling of promises is always sure, yet it is often slow. It was now 215 years since God had promised Abraham to make of him a great nation, ch. 12:2; yet that branch of his seed, to which the promise was made sure, had only increased to seventy, of whom this particular account is kept, to show the power of God in making these seventy become a vast multitude.