Catalyzes the interconversion of 2-phosphoglycerate (2-PGA) and 3-phosphoglycerate (3-PGA) (PubMed:21813794). Required for guard cell function (e.g. blue light-, abscisic acid- (ABA), and low CO(2)-regulated stomatal movements) and fertility (e.g. pollen grains production) (PubMed:21813794). (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. No visible phenotype (PubMed:21813794). Plants missing both PGM1 and PGM2 have no detectable phosphoglycerate mutase activity and show defects in blue light-, abscisic acid- (ABA), and low CO(2)-regulated stomatal movements (PubMed:21813794). The double mutant ipgam1 ipgam2 exhibits a severely impaired vegetative growth with pale reticulate leaves and don't produce pollen (PubMed:21813794). Belongs to the BPG-independent phosphoglycerate mutase family.