I've spent much of my focus as applied to comics in the last decade on Iceman and his connection to the Dragon Mythos, acquiring knowledge and then sharing that knowledge with receptive Iceman fans. That has meant delving a great deal into the Phoenix Mythos(I spent the 80's somewhat obsessed with Jean and Rachel so it wasn't exactly foreign territory), so I can provide some informed knowledge of the following:
White Phoenix of the Crown
The term is derived from the Hebrew Kabbala.
The White represents an aliment between the two sides. Kabbalah divides everything in the world into either Sitra D’Kedushah (the side of holiness represented by White) or Sitra Achra (the side of impurity represented by Black)—literally meaning “the other side,” or the side of Kelipah.
The Phoenix corresponds in this case to an Archangel of divine realms called the Sefirot, specifically the Archangel Michael.
The Crown is a reference to the canopy of a tree, in this case the Tree of Life and Death. The Crown is the Divine/Life side and is comprised of the ten realms of the Sefirot. The 'White Hot Room' is one of the Sefirot, specifically תִּפְאֶרֶת, frequently transliterated as Tiferet or Tiphareth.
Hope this helps.