Catalyzes the addition of a mannose residue from GDP-D-mannose to GlcAGroAc2 to generate 1,2-di-O-C16/C18:1-(alpha-D-mannopyranosyl)-(1-4)-(alpha-D-glucopyranosyluronic acid)-(1-3)-glycerol(ManGlcAGroAc2). Phospholipid metabolism; phosphatidylinositol metabolism. Belongs to the glycosyltransferase group 1 family.