I used to think they were 'just bag carriers', too, but caddies at every level have to know their shit. At the pro level, they're like a good Chief Boatswain's Mate - the skipper doesn't succeed without them.
He does, however, need to understand that the eagle does not chase the fly. It would be one thing if he were defending his guy, but he wasn't. He just wanted to attack Phil and there's no point in that - he's attached to the guy at the top of the totem pole. Why not just enjoy that success while it lasts instead of acting petty and sophomorish?