Catalyzes the transfer of an acyl group from acyl-phosphate (acyl-PO(4)) to glycerol-3-phosphate (G3P) to form lysophosphatidic acid (LPA). This enzyme utilizes acyl-phosphate as fatty acyl donor, but not acyl-CoA or acyl-ACP. an acyl phosphate + sn-glycerol 3-phosphate = a 1-acyl-sn-glycero-3-phosphate + phosphate Lipid metabolism; phospholipid metabolism. Probably interacts with PlsX. Belongs to the PlsY family.