Catalyzes the interconversion of 2-phosphoglycerate and 3-phosphoglycerate. (2R)-2-phosphoglycerate = (2R)-3-phosphoglycerate Carbohydrate degradation; glycolysis; pyruvate from D-glyceraldehyde 3-phosphate: step 3/5. Homodimer. Belongs to the phosphoglycerate mutase family. BPG-dependent PGAM subfamily. Extended N-terminus.