The key to this is how Phoenix is using her powers. When she is using them all and at full control then she becomes a cosmic thing.
Usually she focuses on one aspect at a time to full measure and THAT could be of use to someone with Wonder Woman's varied set (magic and strength...same for Thor when he is actually thinking his way through the fight) or to someone who can best her at her best in one area (The Hulk's strength). Another advantage the Hulk has is his MPD and the fact that tackling his screwed-up mind has increasingly become a losing proposition for anyone who has tried it.
If I went with a Big Six to take her on I would go with Hulk, Ghost Rider, Silver Surfer, Wonder Woman, Green Lantern, Dr. Fate.