Catalysis of the reaction: UDP-4-deoxy-4-formamido-beta-L-arabinopyranose + ditrans,octacis-undecaprenyl phosphate = UDP + 4-deoxy-4-formamido-alpha-L-arabinopyranosyl ditrans,octacis-undecaprenyl phosphate.
undecaprenyl-phosphate Ara4FN transferase activity