2 things I found about this:

1. apparently Saya in an interview keyfabe blamed Utami for this, saying she chose to abandon QQ like she abandoned Stardom. If this is the real rationale they’re gonna go with it feels like such a petty reason to disband a beloved unit, especially since what are the odds this will ever actually be resolved given there is no fucking way they’ll have a working relationship.

2. She spelled her new nickname “Phenex” not “Phoenix” and it doesn’t seem to be an accident since she has both in her tweet. This is Phenex.

Note that “Phenex hopes to return to Heaven after 1,200 years.”

Could be foreshadowing, could be a coincidence. Guess we’ll find out.

What I do know is that the Ars Goetia is a recurring trope in anime and Japanese media in general and it’s treated as a grab bag of monsters and less obvious symbolism since it’s not something people are immediately familiar with but easily googled.