I saw that last scene as both "marking territory" and expression of affection. Phillip was jealous (the nuances in Tobias' facial expressions are just amazing. who needs a monologue!). It was actually fun to watch a ladies' man being threatened by a "nice boy" lol
He went in for that kiss as a mature adult's version of a tantrum. Subdued anger and affection in one. Yes it was him kissing his wife to assert his position, but it was also to express and "remind her" that he does love and care for her.
I'm still amazed at the casting of Menzies. When i saw photos of him in make up next to Phillip of those times, i though, i guess, it's close-ish... I was down for him as Phillip though cause I adore him. Bu that grin when he was leaving her office, with his face half obscured by shadow, i swear, for a split second i thought Prince William is gonna emerge into a fully lit part of the scene.