"A great tactician creates plans.
A good tactician recognizes the soundness of a plan presented to him.
A fair tactician must see the plan succeed before offering approval.
Those with no tactical ability at all may never understand or accept the plan.
Nor will such people understand or accept the tactician.
To those without that ability, those who possess it are a mystery.
And when a mind is too deficient in understanding, the resulting gap is often filled with resentment."
Galactus would be able to overcome The Phoenix Force with the huge amount of Power Cosmic he has. Galactus isn't the strongest being in MArvel in fact he is owned too much. But I see no way of Phoenix to beat The World Devourer...
In the first set of scans, Galactus was indeed hungry, but if you actually bothered to read and analyse what was being said as opposed to being an airhead and focusing on the artwork, you'd see Galactus illustrate his limitations as opposed to a being like Phoenix.
He is a limited being. He requires external sustenance. He eats, he exerts, he uses up that energy and needs to eat another planet. Phoenix on teh other hand is hooked up to an unlimited energy source, so while Galactus may be able to hang with her for all of a few seconds, he would eventually use up all his resources whilst she would carry on strong.
Read the scans.
As for the second case. Jean was weak as well. In that story instead of killing herself at the end of the Dark P Saga, she had a psychic lobotomy, which removed all of the psychic parts of her brain. She lost her powers.
Then as Cyclops was getting pounded something within her clicked and she gained them again, however she stated that she was weak and at that point she had limits and if even could match those current limits it was Galactus. However at the same time she said her power was getting stronger the more and more she used it.
She faced Galactus and dominated the battle. His energy blasts did nothing to her, whilst hers made him cry out in pain. He retreated claiming that if he stayed he would beat Phoenix.
Claims that went unproven and claims that became irrelevant when Phoenix eventually gained all of her power back and she was corrupted again and consumed by her dark side, lashing out and consuming the universe.