Phosphatase that acts on lipids with a phosphoinositol headgroup (PubMed:11676921). Has phosphatase activity towards phosphatidylinositol 3-phosphate and phosphatidylinositol 3,5-bisphosphate (PubMed:11676921). May also dephosphorylate proteins phosphorylated on Ser, Thr, and Tyr residues (PubMed:10733931). 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 a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-3,5-bisphosphate) + H2O = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-5-phosphate) + phosphate H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate 1,2-dihexadecanoyl-sn-glycero-3-phospho-(1D-myo-inositol-3-phosphate) + H2O = 1,2-dihexadecanoyl-sn-glycero-3-phospho-(1D-myo-inositol) + phosphate 1,2-dihexadecanoyl-sn-glycero-3-phospho-(1D-myo-inositol-3,5-phosphate) + H2O = 1,2-dihexadecanoyl-sn-glycero-3-phospho-(1D-myo-inositol-5-phosphate) + phosphate 1,2-dioctanoyl-sn-glycero-3-phospho-(1-D-myo-inositol-3-phosphate) + H2O = 1,2-dioctanoyl-sn-glycero-3-phospho-(1D-myo-inositol) + phosphate Belongs to the protein-tyrosine phosphatase family. Non-receptor class myotubularin subfamily.