Catalyzes the NAD-dependent oxidation and subsequent decarboxylation of D-threonate 4-phosphate to produce dihydroxyacetone phosphate (DHAP). Can also use 4-hydroxy-L-threonine 4-phosphate as substrate. 4-O-phospho-D-threonate + NAD(+) = CO2 + dihydroxyacetone phosphate + NADH Binds 1 divalent metal cation per subunit. kcat is 6.9 sec(-1) with D-threonate 4-phosphate as substrate. kcat is 2.2 sec(-1) with 4-hydroxy-L-threonine 4-phosphate as substrate. Homodimer. Belongs to the PdxA family. PdxA2 subfamily.