X-Men: What Happened To Everyone Who Became The Phoenix?
4. Emma Frost
The former White Queen has been possessed by the Phoenix Force not once but twice. During 'Endsong', the Phoenix arrives on Earth with the specific intent of using up Cyclops so it can recharge itself.
As the X-Men try to defeat it, it becomes obvious to Emma that the only way she can save the man she loves is to offer herself up as a host. Doing so she finds out that the power is far too great and a now-not-dead-again-for-the-millionth-time version of Jean Grey forces the Phoenix from her.
The second time the Phoenix comes for her is during the Avengers vs. X-Men story, which seems to be where a lot of the characters on this list get their time with the force. Attempting to destroy the Phoenix Force with his usual science-first-ask-questions-later approach, Tony Stark only manages to split it into five parts.
These separate pieces inhabit the bodies of the group that becomes the Phoenix Five - which includes Emma Frost. The problem here is that, as she slowly becomes more powerful, she starts to lean more and more towards the dark side. It's only when she's defeated by Hope Summers that she's saved.