If Paige does know, which is likely although Philip was never as much as part of her training as Elizabeth was, then what does she think about it?

Here she is, risking her freedom - and if it's not clear that it's also risking her life too after this episode, it never will be - for an abstract notion and there he is stopping helping defend his motherland, the country of his birth.

If he's prepared to do that, why wouldn't he be prepared to betray them?

(One of the options for the 'what happens in the end' poll: Philip attempts to save Paige and/or Elizabeth from something by turning, and probably fails to do so...)