Phosphotransfer between the C1 and C5 carbon atoms of pentose. alpha-D-ribose 1-phosphate = D-ribose 5-phosphate 2-deoxy-alpha-D-ribose 1-phosphate = 2-deoxy-D-ribose 5-phosphate Binds 1 or 2 manganese ions. Metabolic intermediate biosynthesis; 5-phospho-alpha-D-ribose 1-diphosphate biosynthesis; 5-phospho-alpha-D-ribose 1-diphosphate from D-ribose 5-phosphate (route II): step 1/3. Belongs to the phosphopentomutase family.