Phosphatase that specifically dephosphorylates phosphatidylinositol 3-phosphate (PtdIns(3)P) and inositol 1,3-bisphosphate (Ins(1,3)P2). a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-3-phosphate) + H2O = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol) + phosphate 1D-myo-inositol 1,3-bisphosphate + H2O = 1D-myo-inositol 1-phosphate + phosphate Interaction with MTMR9 increases phosphatase activity. Heterodimer (via C-terminus) with MTMR9 (via coiled coil domain); the interaction enhances MTMR7 catalytic activity (By similarity). Does not homodimerize (By similarity). Interacts with RAB1B (in GDP-bound form) (By similarity). May partially localize to endosomes and/or the Golgi apparatus. Expressed specifically in brain. Belongs to the protein-tyrosine phosphatase family. Non-receptor class myotubularin subfamily.