Removes the 4'-phosphate group from lipid A species. Absence of phosphate groups in lipid A renders the bacteria resistant to host-derived cationic antimicrobial peptides (CAMP) and allows it to camouflage itself from the host innate immune response (PubMed:19552698, PubMed:20657724). Removal of the 4'-phosphate may be required to generate the substrate for deacylation of the pentaacyl lipid A to the tetraccylated lipid A species (PubMed:19552698). Bacterial outer membrane biogenesis; LPS lipid A biosynthesis. No longer responds to changes in hemin, decreased removal of 4'-phosphate from lipid A species. Accumulates pentaacylated 4'-phosphate lipid A with concomitant loss of the usual non-phosphorylated tetraacylated lipid A. Lipopolysaccharide (LPS) or bacteria from this strain are a somewhat potent inducer of the human innate immune response via Toll-like receptor 4 (TLR4) in cultured HEK293 cells; double lpxE-lpxF mutants are more potent. Loss of resistance to the cationic antimicrobial peptide (CAMP) polymyxin B. Double lpxE-lpxF mutants accumulate multiple mono- and bi-phosphorylated lipid A species (PubMed:19552698, PubMed:20657724). Unable to colonize rabbit periodontium, a model for periodontal disease (PubMed:24478080). When grown in low hemin conditions the major lipid A species are non-phosphorylated tetraacyl and 4'-phosphate pentaacyl lipid A, while under high hemin conditions the major lipid A species are non-phosphorylated tetraacyl and 1-phosphate tetraacyl lipid A (hemin is protoporphyrin IX containing Fe(3+) with a chloride ligand (CHEBI:50385) involved in the change from healthy to diseased gums). Belongs to the lipid A LpxF 4'-phosphatase family.