Albert Barnes Commentary 1 Kings 22:32

"And it came to pass, when the captains of the chariots saw Jehoshaphat, that they said, Surely it is the king of Israel; and they turned aside to fight against him: and Jehoshaphat cried out." — 1 Kings 22:32 (ASV)

Surely it is the king of Israel—This was a natural assumption, as Jehoshaphat was the only one wearing royal robes.

And Jehoshaphat cried out—Jehoshaphat called to his men for help, perhaps using his own special battle cry, which would have been distinct from Ahab’s and likely known to the Syrians.