I have two that would know Philip, but Kris (this journal) would likely have had the most interaction with him. He's pretty much everything Kris does not want to be (down to the fear of being forced into the military or politics). But he'd be friendly with Philip and very much, "Better you than me!" about it all.
I also have Vera, verily, princess of Slovenia & Croatia. She's secretly a rebel, but would be polite to Philip. I'm not sure if they would have much history beyond that, but I'm open to suggestions if you think of any.