My favorite example is "trophy".This is interesting. It's Nepos in Latin but the French was like "Let's confuse our people by using ph." Thanks for the lesson.
It's from Greek "τρόπαιον", which never had a "phi"/φ in it. It came to Latin as "tropaeum", where it later became "trophaeum", and we now know it as "trophy".
It does have a Greek origin, so the rule of thumb works for it, but the Greeks didn't give its now familiar "f" ("ph") sound, since it never had a phi over there. The Romans did. And it was through Latin that it arrived in English.