Lipid phosphatase that has high specificity for phosphatidylinositol 3-phosphate and has no activity with phosphatidylinositol 4-phosphate, phosphatidylinositol (4,5)-bisphosphate and phosphatidylinositol (3,4,5)-trisphosphate (, ). Activity with phosphatidylinositol (3,5)-bisphosphate is controversial; it has been shown by , while  find no activity with this substrate.
Subcellular locations: Cell membrane, Cytoplasm