Specifically dephosphorylates nucleoside 5'-monophosphates to nucleosides and inorganic phosphate. Displays high activity toward 5'-UMP and 5'-IMP, significant activity against 5'-XMP and 5'-TMP, and low activity against 5'-CMP. a ribonucleoside 5'-phosphate + H2O = a ribonucleoside + phosphate Divalent metal cation. Prefers Mn(2+) over Mg(2+). Optimum pH is 7.4. Belongs to the HAD-like hydrolase superfamily.