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 (e.g. toward Golovinomyces cichoracearum) by promoting sphingolipid metabolism and regulating ceramide accumulation (By similarity). Belongs to the sphingomyelin synthase family.