Dephosphorylates several organic phosphate monoesters such as 3'-UMP, 5'-UMP and pNPP (PubMed:6256351). Also has a phosphotransferase activity catalyzing the transfer of low-energy phosphate groups from organic phosphate monoesters to free hydroxyl groups of various organic compounds such as the 2'-, 3-, or 5'-hydroxyls of nucleosides and nucleotides (PubMed:3049613). Also displays significant phosphomutase activity since it is able to catalyze the transfer of the phosphate group of 3'-AMP from the 3'-position both to the 2'- and 5'-positions. One of the physiological functions of the phosphohydrolytic activity of the enzyme is believed to be the scavenging of organic phosphate esters that otherwise cannot pass the cytoplasmic membrane (PubMed:6256351). a phosphate monoester + H2O = an alcohol + phosphate Binds 1 Mg(2+) ion per subunit. Nucleosides, and particularly 2'-deoxyribonucleosides, are potent inhibitors of the phosphatase activity. The phosphatase activity is also inhibited by inorganic phosphate and EDTA in vitro. Optimum pH is 5.0-5.5 and 6.5 for the phosphatase activity with 3'-UMP and 5'-UMP as substrate, respectively. Homotetramer. Cells lacking this gene show a severely decreased growth rate on 5'-UMP as pyrimidine source. Belongs to the class B bacterial acid phosphatase family.