Catalyzes the conversion of GlcNAc-6-P into GlcNAc-1-P during the synthesis of uridine diphosphate/UDP-GlcNAc, a sugar nucleotide critical to multiple glycosylation pathways including protein N- and O- glycosylation. {ECO:0000303|PubMed:24589341, ECO:0000303|PubMed:24698316, ECO:0000303|PubMed:24931394}. This is the function of PGM3 (phosphoglucomutase 3, ENSG00000013375).