Somewhere there is bound to be a helpful book on angel/headvirus etiquette, all the information laid down and lovingly elaborated on. A set of strict yet vital rules... of which Castiel probably broke just about all and then some.

From being in Philip's head in the first place to indulging Clarence with an answer to making it that answer and then going on...

It's hard for Philip to pick between incredulous, mortified and furious when they all apply in such significant amounts.

So he simply bites his lip, lowers his head and walks a whole lot faster.