Catalyzes the interconversion of 2-phosphoglycerate and 3-phosphoglycerate. (2R)-2-phosphoglycerate = (2R)-3-phosphoglycerate Binds 2 manganese or magnesium ions per subunit (By similarity). Cobalt and nickel are less efficient (PubMed:17897734). Activity is not affected by 2,3-bisphosphoglycerate. Optimum pH is 7.5-8.5. Optimum temperature is 22 degrees Celsius. Active between 17 and 32 degrees Celsius. Carbohydrate degradation; glycolysis; pyruvate from D-glyceraldehyde 3-phosphate: step 3/5. Expressed ubiquitously. High expression levels in the nerve ring region, intestine and body wall muscles. RNAi knockdown results in embryonic lethality. The few surviving larvae have sluggish movements, abnormal body morphology, developmental arrest and impaired survival. Belongs to the BPG-independent phosphoglycerate mutase family.