Actually, you raise an interesting point. Pheonix's power stems (at least in Grant Morrison's version) from a sort of all-encompassing telekenesis. From what I've read, Pheonix can basically move molecules about any way she pleases and thereby reshape reality as she desires.
On the other hand....
Absolute Zero means all matter stops moving. Can Pheonix break through that inertia, through sheer will force the molecules to respond? Or does frozen mean frozen? Interesting idea.