Sure I can o___o
If you're dating someone exclusively there are certain boundaries. I mean if they HADN'T said they liked him, I would agree wholeheartedly that she should back off and let him have his friends. But once they crossed that line, they're no longer JUST friends, no matter what he may claim. He'll always see them as potential girlfriends/hook-ups because he knows they want to go there with him. Even if nothing came of it, he's--you said it perfectly--emotionally cheating.
EDIT: Also, the fact that he likes to look through her phone, but not let her look through his, makes me think that he knows he's doing something wrong by talking to girls who like him as more than a friend. Guilty conscience.