The enzyme catalyses a step in the assembly of the repeating-unit of the O-antigen of the Gram-negative bacterium?Aeromonas hydrophila?AH-3. The enzyme shows no activity with UDP-N-acetyl-¦Á-D-glucosamine (cf. EC?2.7.8.33, UDP-N-acetylglucosamine-undecaprenyl-phosphate?N-acetylglucosaminephosphotransferase).