Has been shown, in vitro, to act on Ser, Thr and Tyr-phosphorylated substrates. H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 manganese ions per subunit. Belongs to the PPP phosphatase family.