"Classic" Rachel did about as well against Galactus as Strange did. She wasn't nearly powerful enough to even pose a threat to the Beyonder, even after he powered her up. Wolverine nearly killed "classic" Rachel, and she couldn't mentally shut Wolverine down during Enemy of the State. Xavier mentally defeated Phoenix Force Jean, and Xavier was unable to penetrate Strange's psychic defenses at all.
So Rachel at her absolute most powerful is the Phoenix, which as GS said, is the most powerful being in the entire universe or whatever, but Rachel's average and most recent showings are far from that. That's the only version we should be debating, here, for the same reason we shouldn't use Keeper Surfer feats or Blood and Thunder Thor feats on their threads.