Catalyzes the interconversion of 2-phosphoglycerate and 3-phosphoglycerate. (2R)-2-phosphoglycerate = (2R)-3-phosphoglycerate Binds 2 manganese ions per subunit. Carbohydrate degradation; glycolysis; pyruvate from D-glyceraldehyde 3-phosphate: step 3/5. Monomer. Probably essential, it was not disrupted in a global transposon mutagenesis study. Belongs to the BPG-independent phosphoglycerate mutase family.