Catalysis of the reaction: UDP-N-acetyl-alpha-D-glucosamine + UDP-D-galactose = H+ + UDP-N-acetyl-6-(D-galactose-1-phospho)-D-glucosamine + UMP.
uridine diphosphogalactose-uridine diphosphoacetylglucosamine galactose-1-phosphotransferase activity