Catalyzes the addition of a single ribitol phosphate unit onto the glycerol phosphate of the linkage unit, as a primer for polymerisation by TarL. 4-O-[(2R)-glycerylphospho]-N-acetyl-beta-D-mannosaminyl-(1->4)-N-acetyl-alpha-D-glucosaminyl di-trans,octa-cis-undecaprenyl diphosphate + CDP-L-ribitol = 4-O-[1-D-ribitylphospho-(2R)-1-glycerylphospho]-N-acetyl-beta-D-mannosaminyl-(1->4)-N-acetyl-alpha-D-glucosaminyl di-trans,octa-cis-undecaprenyl diphosphate + CMP + H(+) Cell wall biogenesis; poly(ribitol phosphate) teichoic acid biosynthesis. Belongs to the CDP-glycerol glycerophosphotransferase family.