Catalyzes heptose transfer to the lipopolysaccharide core. It transfers the first L-glycero-D-manno-heptose to the phosphorylated 3-deoxy-alpha-D-manno-octulosonic acid (Kdo-P) of the inner core. Bacterial outer membrane biogenesis; LPS core biosynthesis. Belongs to the glycosyltransferase 9 family.