To spawn these guys, a Priest (SHM,DRU,CLR) with a Tailoring kit needs to hail the Phantasmal Priest and go through the text to get 4 x Dried Segment of Flesh. Trivial is about >158 per sources. Once the Priest turns in the combined item: Parchment of Flesh to the Phantasmal Priest there is more text that ports him/her to a room to pick up 2 ground spawns.
Feed the ground spawns (Stone of something ...) to each Guardian. Once the 2nd is turned in, the Priest will be crushed.