Albert Barnes Commentary 2 Chronicles 28:12

"Then certain of the heads of the children of Ephraim, Azariah the son of Johanan, Berechiah the son of Meshillemoth, and Jehizkiah the son of Shallum, and Amasa the son of Hadlai, stood up against them that came from the war," — 2 Chronicles 28:12 (ASV)

“Ephraim” is used here in the generic sense so common in the prophets, as a synonym for the ten tribes.