Probably removes the 4'-phosphate moiety from lipid A species. Not seen to act on other membrane components, nor does it dephosphorylate the 1-phosphate group of lipid A and/or lipid A precursors. Bacterial outer membrane biogenesis; LPS lipid A biosynthesis. Lipid A contains a monophosphate group at position 4' instead of the usual galacturonic acid moiety. No longer has 4'-dephosphorylase activity on Kdo(2)-lipid IV(A). Increased sensitivity to the cationic antimicrobial peptide (CAMP) polymyxin B (PMB) but not to other several other antibiotics. A double lpxE-lpxF mutant contains lipid A bi-phosphorylated at positions 1- and 4'- and has greater sensitivity to PMB than either single mutant. No visible effect on free-living bacteria, or on nitrogen fixation upon nodulation of P.vulgaris. In this strain lipid A lacks phosphate groups, instead contains a galacturonic acid moiety at position-4' in place of the monophosphate group found in E.coli. Belongs to the lipid A LpxF 4'-phosphatase family.