The phillipt Level Theme is the name of the Level Theme that was used in FredCast. It is unknown if any other levels used these textures. The name comes from the level designer, Phillip Wheeler, who often went by his username "phillipt".
It appears that this theme is intended to be a modified version of idBase. Some textures share the same names and the .WAD file used to compile it was called "base.WAD" as idBase normally would be. This suggests that this Level Theme is a subtype of Base.