Involved in phosphonate degradation. H2O + phosphonoacetaldehyde = acetaldehyde + H(+) + phosphate Binds 1 Mg(2+) ion per subunit. Homodimer. Belongs to the HAD-like hydrolase superfamily. PhnX family. The first enzyme involved in phosphonate degradation (PhnW, EC 2.6.1.37) is not found in this organism. The function of this enzyme is therefore uncertain.