This is an ongoing build for the new patch released 24 January 2017.  I am currently able to facetank Cosmic Midtown bosses.  More details to come as I refine the build, including videos.  I am listing my actual equipment in the build, since it is often difficult for people to get all the best gear - this is easily achievable with little effort in midtown or hightown.

This build will allow you to remain in Dark Phoenix form for the entire fight, granting a bonus of 15% damage, 100% Spirit cost reduction, Immunity to Crowd Control, and 15% extra healing from all sources.  Using Pyrokinetic Barrier and Phoenix Drain as your main Phoenix force generators, use your other powers as available and melt everything in your area of effect.  Phoenix Drain regens 1400 health per second, with a 15% increase from Dark Phoenix.  Before adding Infinity powers or gear, you are getting 1610 health per second.  In addition, activating Dark Phoenix grants a 100% spirit reduction for the entire duration so there go any spirit issues we may have, allowing us to further focus on damage and area radius.

I use Friends of the First Class rather than Telepathic Dominance (2nd row of talents) to gain the Strengthened Buff and for the Taunt effect.  Font of Power allows Dark Phoenix to remain active while building the Phoenix force necessary to reuse it, Phoenix Ascending allows Phoenix Drain to generate Phoenix force and negates all our Spirit issues and Controlled Engagement turns Pyrokinetic Barrier into our main Phoenix force generator and provides a nice guaranteed crit every 5 seconds, plus a Weaken on nearby enemies and a small damage shield.

Debris Storm acts like a Signature Power, causing almost 70k damage twice per second for 4 seconds with a 45 second cooldown. This will be our big hitter, along with Crushing Telekinesis causing up to 45k per hit for 5 hits.  With Dark Phoenix active, add 15% damage on top of this and you can get an idea of how hard Jean can consistently hit everything in her aoe!