Catalyzes the transfer of the L-Ara4N moiety of the glycolipid undecaprenyl phosphate-alpha-L-Ara4N to lipid A. The modified arabinose is attached to lipid A and is required for resistance to polymyxin and cationic antimicrobial peptides (By similarity). 4-amino-4-deoxy-alpha-L-arabinopyranosyl di-trans,octa-cis-undecaprenyl phosphate + lipid IVA = lipid IIA + di-trans,octa-cis-undecaprenyl phosphate. Lipopolysaccharide metabolism; 4-amino-4-deoxy-beta-L-arabinose-lipid A biosynthesis. Activated by low magnesium concentrations, via the two-component regulatory system PhoP/PhoQ. Belongs to the glycosyltransferase 83 family.