Catalyzes the transfer of the cytidylyl group of CTP to sn-glycerol 3-phosphate so the activated glycerol 3-phosphate can be used for teichoic acid synthesis, via incorporation into both the linkage unit by TarB and TarF. CTP + H(+) + sn-glycerol 3-phosphate = CDP-glycerol + diphosphate Cell wall biogenesis; poly(ribitol phosphate) teichoic acid biosynthesis. Homodimer. Belongs to the cytidylyltransferase family.