Catalyzes the conversion of glucosamine-6-phosphate to glucosamine-1-phosphate (By similarity). Does not display phosphoglucomutase (PGM) or phosphomannomutase (PMM) activities. alpha-D-glucosamine 1-phosphate = D-glucosamine 6-phosphate Binds 1 Mg(2+) ion per subunit. Activated by phosphorylation. Belongs to the phosphohexose mutase family.