Involved in the degradation of galactose via the DeLey-Doudoroff pathway. Catalyzes the reversible, stereospecific retro-aldol cleavage of 2-keto-3-deoxy-6-phosphogalactonate (KDPGal) to pyruvate and D-glyceraldehyde-3-phosphate (By similarity). 2-dehydro-3-deoxy-6-phospho-D-galactonate = D-glyceraldehyde 3-phosphate + pyruvate Carbohydrate acid metabolism; D-galactonate degradation; D-glyceraldehyde 3-phosphate and pyruvate from D-galactonate: step 3/3. Homotrimer. Cells lacking this gene fail to grow on galactose as sole carbon source. Belongs to the KHG/KDPG aldolase family.