Hydrolyzes the ester bond at the sn-1 position of glycerophospholipids and produces 2-acyl lysophospholipids. Hydrolyzes phosphatidylserine (PS) in the form of liposomes and 1-acyl-2 lysophosphatidylserine (lyso-PS), but not triolein, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA) or phosphatidylinositol (PI). 1-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine + H2O = (9Z)-octadecenoate + H(+) + sn-glycero-3-phospho-L-serine 1,2-di-(9Z)-octadecenoyl-sn-glycero-3-phospho-L-serine + H2O = (9Z)-octadecenoate + 2-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine + H(+) 1-hexadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-phospho-L-serine + H2O = 2-(5Z,8Z,11Z,14Z)-eicosatetraenoyl-sn-glycero-3-phospho-L-serine + H(+) + hexadecanoate Belongs to the AB hydrolase superfamily. Lipase family.