Catalyzes the reversible oxidation of 3-phospho-D-glycerate to 3-phosphonooxypyruvate, the first step of the phosphorylated L-serine biosynthesis pathway. Does not catalyze the reversible oxidation of 2-hydroxyglutarate to 2-oxoglutarate and the reversible oxidation of (S)-malate to oxaloacetate. (2R)-3-phosphoglycerate + NAD(+) = 3-phosphooxypyruvate + H(+) + NADH Amino-acid biosynthesis; L-serine biosynthesis; L-serine from 3-phospho-D-glycerate: step 1/3. Homotetramer. Decreased level of free serine, glycine, taurine, GABA, glutamine, and threonine in spinal cord and head. Impaired central nervous system (CNS) with shorter neural tube length and overall growth retardation. Severe atrophy at the thoracic level, particularly in the dorsal spinal cord. Poorly developed dorsal horn and adjacent mantle zone. Neurons fail to develop neurites, particularly commissural axonal fibers. Belongs to the D-isomer specific 2-hydroxyacid dehydrogenase family.