Interconverts GlcNAc-6-P and GlcNAc-1-P. 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. Belongs to the phosphohexose mutase family. Sequencing errors.