Probably catalyzes the addition of a phosphoethanolamine moiety to the dephosphorylated 1-position of the disaccharide backbone of lipid A. Lipid A that is 1-phosphorylated is not a substrate for this enzyme. Bacterial outer membrane biogenesis; LPS lipid A biosynthesis. In this organism most lipid A is tetraacylated without a phosphate group at the 4'-position and has a phosphoethanolamine residue at the 1-position. Belongs to the phosphoethanolamine transferase family. EptA subfamily.