Any kind of light AA support will make using Phoenixes against armies quite inefficient. I don't think a Phoenix with a good attack would really remove unit blobs or skirmisher lines as long as people know how to AA.
What it could do though is start shutting down raids pretty hard. Mixing in AA into a slower main army is easy since it can keep up with it, but people rarely add AA to their raiding parties at least partly due to the speed difference between raiders and AA units.
Currently, Phoenix is mainly a defensive tool and actually isn't very bad at it. Its fragility makes it unsuited for any kind of offensive use though.
Planes ability to shut down raids with ease has been something that has got a lot of criticism in the past (stun-Stiletto, speed dive Raven). Making Phoenix attack better would probably just bring back the old situation with Planes being too easy of a solution against raids.
Then again, it's not like gunships aren't superb at shutting down raids.