What the Bible says about Ephraim as the Ten Northern Tribes
(From Forerunner Commentary)
When God uses the term "Ephraim," He may be referring to the actual family of Ephraim, but it is more likely that He is using it as He uses the term "Jerusalem": for the whole country. Ephraim represents or symbolizes the ten northern tribes, Israel as distinct from Judah, because Ephraim was its leading tribe.
John W. Ritenbaugh
Where Is the Beast? (Part Six)