Catalyzes the conversion of GlcNAc-6-P into GlcNAc-1-P during the synthesis of uridine diphosphate/UDP-GlcNAc, which is a biosynthetic precursor of chitin and also supplies the amino sugars for N-linked oligosaccharides of glycoproteins (PubMed:8174553). Also has phosphoglucomutase activity (PubMed:8119301). N-acetyl-alpha-D-glucosamine 1-phosphate = N-acetyl-D-glucosamine 6-phosphate Binds 1 Mg(2+) ion per subunit. Nucleotide-sugar biosynthesis; UDP-N-acetyl-alpha-D-glucosamine biosynthesis; N-acetyl-alpha-D-glucosamine 1-phosphate from alpha-D-glucosamine 6-phosphate (route I): step 2/2. Results in undivided strings of cells and growth arrest after approximately 5 division cycles. Present with 14700 molecules/cell in log phase SD medium. Belongs to the phosphohexose mutase family.