A question I'm very intersted in someone answering is: When is Galactus NOT hungry? When he's not seen? I just think it's a ridiculous notion to always harp on a fed or full powered Galactus when there is virtually no such thing. Whenever Galactus is having a tiff with someone, he's always hungry--that's when he shows up. I think it's perfectly acceptable form that Galactus be weakened from hunger, because he always is.
And it's pretty obvious that all DP has to do is let Galactus wear himself down. He admits that he can't keep up with the output of Phoenix' power. It's simply a matter of time. And DP can always warp somewhere where there's a nice tasty sun for a snack. Or transport G to a dimension where there would be no nourishment for him.