May dephosphorylate phosphatidylinositol-3-phosphate (PI3P) (PubMed:12788949, PubMed:14565969). In association with mtm-9, plays a role in endosome trafficking probably by regulating phosphatidylinositol-3-phosphate levels (PubMed:14565969, PubMed:21076391). Regulates fluid phase endocytosis in coelomocytes (PubMed:14565969). Controls the endosomal localization of sorting nexin snx-3 and the levels of sorting receptor mig-14 (PubMed:21076391). By regulating the retrograde transport of mig-14, may be involved in the secretion of Wnt ligands such as egl-20 (PubMed:21076391). Regulates posterior migration of QL neuroblast descendants and the anterior migration of QR neuroblast descendants and HSN neurons during larval development (PubMed:21076391). Involved in the formation of correct synapse number in DA9 motor neurons probably in part by regulating the secretion of Wnt ligand egl-20 (PubMed:25479419). 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 1,2-dioctanoyl-sn-glycero-3-phospho-(1D-myo-inositol-3,5-bisphosphate) + H2O = 1,2-dioctanoyl-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 Heterodimer with mtm-9. Expressed in intestinal cells (PubMed:12788949). Expressed in head neurons, pre-anal ganglion, hypodermal cells, anal depressor muscle and non-neuronal cells in the tail (PubMed:25479419). The FYVE domain appears to be dispensable for membrane targeting and activity but may be important to increase avidity to membrane. RNAi-mediated knockdown causes an increase in phosphatidylinositol-3-phosphate at the apical plasma membrane of intestinal cells. Belongs to the protein-tyrosine phosphatase family. Non-receptor class myotubularin subfamily.