Catalyzes the transfer of the phosphorylinositol group from phosphatidylinositol (PI) to phytoceramide, an essential step in sphingolipid biosynthesis. May play an important role in modulating plant programmed cell death (PCD) associated with defense by promoting sphingolipid metabolism and regulating ceramide accumulation. Reduced plant stature. Spontaneous HR-like cell death (SHL). Belongs to the sphingomyelin synthase family.