Hydrolyzes the ester bond of the acyl group attached at the sn-1 position of phosphatidylserines (phospholipase A1 activity) and 1-acyl-2-lysophosphatidylserines (lysophospholipase activity) in the pathway of phosphatidylserines acyl chain remodeling (By similarity). Cleaves phosphatidylserines exposed on the outer leaflet of the plasma membrane of apoptotic cells producing 2-acyl-1-lysophosphatidylserines, which in turn enhance mast cell activation and histamine production. Has no activity toward other glycerophospholipids including phosphatidylcholines, phosphatidylethanolamines, phosphatidic acids or phosphatidylinositols, or glycerolipids such as triolein (By similarity). a 1,2-diacyl-sn-glycero-3-phospho-L-serine + H2O = a 2-acyl-sn-glycero-3-phospho-L-serine + a fatty acid + H(+) 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 a 1-acyl-sn-glycero-3-phospho-L-serine + H2O = a fatty acid + H(+) + sn-glycero-3-phospho-L-serine 1-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine + H2O = (9Z)-octadecenoate + H(+) + sn-glycero-3-phospho-L-serine Belongs to the AB hydrolase superfamily. Lipase family.