Responsible for the provision of inositol required for synthesis of phosphatidylinositol and polyphosphoinositides. Has broad substrate specificity and can use myo-inositol monophosphates, myo-inositol 1,3-diphosphate, myo-inositol 1,4-diphosphate, scyllo-inositol-phosphate, D-galactose 1-phosphate, glucose-1-phosphate, glucose-6-phosphate, fructose-1-phosphate, beta-glycerophosphate, and 2'-AMP as substrates. a myo-inositol phosphate + H2O = myo-inositol + phosphate alpha-D-galactose 1-phosphate + H2O = D-galactose + phosphate Inhibited by Li(+), Ca(2+) and Mn(2+), but also by Mg(2+) at concentrations above 3 mM. Polyol metabolism; myo-inositol biosynthesis; myo-inositol from D-glucose 6-phosphate: step 2/2. Belongs to the inositol monophosphatase superfamily.