Unfortunately, feline tooth resorption is pretty common.
It can be very painful, and if this is the case, all teeth should be removed.
However, not all cats experience discomfort. My vet said that if they are not painful there's no need for a full-mouth extraction. The kitty will end up without teeth, though, since most of them will be resorbed.
Cats without teeth can eat dry food just fine.
All the best to Phoenix and to you!