Re: Galactus vs. The Phoenix Force.
I don't think he can defeat her. I don't think she can defeat him either.
And the stakes would be too high because when Galactus dies, Abraxas gets out. And when Abraxas comes out, he will destroy the multi-verse, unless someone gets ahold of the UN and stops him. LT wouldn't interfere because he believes in the cosmic balance. And Eternity, Death, and Infinity's purpose would be usurped by Abraxas and Oblivion.
When Phoenix dies, the multi-verse would go down with her. Remember what Roma and Death told Galactus? She is the life of the cosmoes apparently. While Galactus is the power of them.