Involved in phosphonate degradation. H2O + phosphonoacetaldehyde = acetaldehyde + H(+) + phosphate Binds 1 Mg(2+) ion per subunit. Inhibited by phosphite, moderately inhibited by phosphonic acids, the corresponding aminophosphonic acids activate the enzyme. Homodimer. By 2-aminoethylphosphonic acid. Belongs to the HAD-like hydrolase superfamily. PhnX family.