I admit I'm conflicted. From one side, I agree with
because Jean is already one of the most powerful mutants (and Earth-based characters in the Marvel Universe) without the need for the additional cosmic uber-power of the phoenix. So I'd permanently bond the Phoenix to a character who isn't too much powerful for themselves - a character who perhaps doesn't have a powerful editorial story. A side-character who can afford to go cosmic and operate on a cosmic level, no more Earth-based. Because I don't think it makes sense for a character-with-phoenix to be involved in "petty" fights on Earth, when they should be involved in cosmic-threats.
But, at the same time, I agree with
So. Who knows!