1) Is this supposed to be Phoenix Taaia fight? Or did @takensteww22 confuse White Phoenix of the Crown (Jean Grey) with Taaia and they merely wanted the strongest Phoenix to be in this battle?

2) That is not White Phoenix. That is just a Phoenix wearing white. Phoenixes tend to pick and choose the costumes they want. Case and point,

Even Emma Frost, who only had a fraction of the Phoenix Force's powers, was wearing white, despite clearly losing her Phoenix power to Cyclops not wearing white.

The only ones who seem to have actually in-canon referred to themselves as a White Phoenix is Hope Summers, which is questionable because she was starting to display Dark Phoenix like personality traits in that moment.

And Jean Grey was the only one officially referred to as a White Phoenix of the Crown and actually held the title.