I'm not sure that's the (sole) rule for "Y as vowel". It acts as a vowel in "fly", "spy", and a few other words. And it seems pretty darn dipthong-like when clustered among vowels, eg "voyeur", "vying".
The word "eye" is an interesting one. It seems to be only vowels, based on pronunciation.
The word "eye" is an interesting one. It seems to be only vowels, based on pronunciation.