Converts N-acetylmannosamine-6-phosphate (ManNAc-6-P) to N-acetylglucosamine-6-phosphate (GlcNAc-6-P). Catalyzes the phosphorylation of N-acetylmannosamine (ManNAc) to ManNAc-6-P. an N-acyl-D-glucosamine 6-phosphate = an N-acyl-D-mannosamine 6-phosphate an N-acyl-D-mannosamine + ATP = ADP + an N-acyl-D-mannosamine 6-phosphate + H(+) Amino-sugar metabolism; N-acetylneuraminate degradation; D-fructose 6-phosphate from N-acetylneuraminate: step 2/5. Amino-sugar metabolism; N-acetylneuraminate degradation; D-fructose 6-phosphate from N-acetylneuraminate: step 3/5. In the N-terminal section; belongs to the NanE family. In the C-terminal section; belongs to the ROK (NagC/XylR) family. NanK subfamily.