Removes the 1-phosphate group from tetra- and probably hexaacylated lipid A species, has no requirement for the Kdo moiety of lipid A (PubMed:15489235). Has no 4'-phosphatase activity (PubMed:15489235, PubMed:16740959). Has no activity on phospholipids (phosphatidylglycerol, phosphatidylethanolamine or cardiolipin). This enzyme has to act before EptA can attach phosphoethanolamine to the 1-position of lipid A (PubMed:16740959). Absence of the 1-phosphate group renders the bacteria partially resistant to host-derived cationic antimicrobial peptides (CAMP), allowing it to camouflage itself from the host innate immune response, and plays a role in the long-term colonization of the host's stomach (By similarity). Does not require divalent cations. Optimum pH is 6.0, activity is seen from pH 5.5 to 8.0. Bacterial outer membrane biogenesis; LPS lipid A biosynthesis. Activity depends on msbA function when expressed in E.coli, strongly suggesting this protein acts in the periplasm (MsbA flips the lipopolysaccharide precursor across the inner cell membrane). Lipid A retains the 1-phosphate group; none of the lipid A species have the usual phosphoethanolamine residue at the 1-position as the enzyme responsible (EptA) cannot act on a phosphorylated residue. In strain 26695 95% is hexaacylated (16 to 18 carbons in length) with both 1- and 4'-phosphate groups, 5% is tetraacylated with only 1-phosphate. In 4 other strains (Cp20-84, Hp7-91, Hsp110-93 and J99) only the 1-phosphate tetraacylated species is seen. Over 1250-fold decrease (strain 26695) or 10-fold decrease (strain Hp7-91) in resistance to cationic antimicrobial peptide (CAMP) polymyxin B (PMB); strain 26695 is probably more sensitive because it has a more negatively charged cell surface and thus binds more CAMP. In strain Hp7-91 upon exposure to PMB the cells round into a coccoid form, the outer membrane forms ruffles, invaginates and in some cases the periplasmic region increases in volume. In this organism most lipid A is tetraacylated without a phosphate group at the 4'-position and a phosphoethanolamine residue at the 1-position. Belongs to the lipid A LpxE 1-phosphatase family.