Based on X-Men: The Last Stand. Probably somewhat inaccurate, so I apologize for that.
What most people don't realize is phoenixes look exactly like other birds. They don't stand out, they fit in with the rest of the group, and there is no way to tell they are any different. No way to tell until they burst into flames.
Or, to put things another way, until it is aflame, how would a phoenix know that is was a phoenix at all?
If she had ever stopped to consider the matter, she would find it ironic that she had been reborn in a flood rather than flames. However, she never stopped to consider anything now. She was made of the flames of her rebirth, destructive and passionate, ready to destroy and burn anything that stood in her way.
She could feel her other self, the plain bird Jean, trapped behind a wall of fire in her mind, as she had been trapped for many years, waiting for the fire that would allow her to be reborn. Now it was her turn to shine, no not to shine, to burn and watch the world burn with her.
The Phoenix knew that she could lose her freedom; Jean could be her undoing. She couldn't let her take over again. Jean wasn't weak, especially helped by the Professor, Jean was strong. However, she was stronger, and she would win.
How does one destroy their other half? She couldn't touch Jean, nor use their formidable power against her, but finally the Phoenix found the perfect solution. Could she break Jean, end the battle before it started? Could she twist Jean's formidable mind until the way to control would be forever lost?
Yes, that was the only way. First move was the strange man with the fire eyes, Jean had loved him, the Phoenix knew this. She quelled his power, saw his sea blue eyes and kissed him. She gave Jean a little access, not too much but enough, she had to be careful, one mistake could trap her again, douse her flames before the rebirth was complete. Jean felt the kiss too, Cyclops still wondering if this could possibly real, and herself seizing the opportunity. The Phoenix kissed him as Jean never had, with none of the tenderness that had shaped their relationship, but pure, raw passion flowing through the conduit of her body into him.
She let Jean feel the kiss, and the false belief that it would all work out. She felt her smile to see his joy at her resurrection, and Jean tried to take control to greet him herself, to kiss him with her mind behind their lips.
The Phoenix then struck, using their power that she had unleashed, the full force of it now emerging from her subconscious. Cyclops dissipated like warm breath on a winter's day and the Phoenix smiled triumphantly. She could feel Jean screaming, her grief ringing through their mind non-stop, like an alarm that wouldn't stop going off. She had won the battle, now time to win the war.
For a phoenix to rise, the bird before has to burn.
Thanks for reading! Reviews are always appreciated.