Lipid phosphatase that specifically dephosphorylates the D-3 position of phosphatidylinositol 3-phosphate and phosphatidylinositol 3,5-bisphosphate, generating phosphatidylinositol and phosphatidylinositol 5-phosphate (PubMed:10733931, PubMed:11302699, PubMed:11676921, PubMed:12646134). Decreases the levels of phosphatidylinositol 3-phosphate, a phospholipid found in cell membranes where it acts as key regulator of both cell signaling and intracellular membrane traffic (PubMed:11302699, PubMed:11676921, PubMed:12646134). Could also have a molecular sequestering/adapter activity and regulate biological processes independently of its phosphatase activity. It includes the regulation of midbody abscission during mitotic cytokinesis (PubMed:25659891). {ECO:0000269|PubMed:10733931, ECO:0000269|PubMed:11302699, ECO:0000269|PubMed:11676921, ECO:0000269|PubMed:12646134, ECO:0000269|PubMed:25659891}. This is the function of MTMR3 (myotubularin related protein 3, Ensembl gene identifier ENSG00000100330).