Lipid phosphatase that specifically dephosphorylates the D-3 position of phosphatidylinositol 3-phosphate (PtdIns(3)P) and inositol 1,3-bisphosphate (Ins(1,3)P2). . This is the function of Ensembl gene identifier ENSG00000003987 (MTMR7, myotubularin related protein 7).