Some additional sources that might help the reader understand Phil’s work, in no particular order.
An in-depth examination of the Rosicrucian Brotherhood:
The Chymical Wedding of Christian Rosenkreutz (pdf format):
The Bardo Thodol audiobook:
The Nag Hammadi Library (html format):
The site this is on, the Gnosis Archive, is also one of the best sources for Gnostic texts on the Web and I have used and linked to it multiple times here.
More to come. Much more.