Catalyzes the interconversion of 2-phosphoglycerate and 3-phosphoglycerate. (2R)-2-phosphoglycerate = (2R)-3-phosphoglycerate (2R)-3-phospho-glyceroyl phosphate = (2R)-2,3-bisphosphoglycerate + H(+) Homodimer. Belongs to the phosphoglycerate mutase family. BPG-dependent PGAM subfamily.