Catalyzes the transfer of CDP-ribitol to the distal N-acetylgalactosamine of the phosphorylated O-mannosyl trisaccharide (N-acetylgalactosamine-beta-3-N-acetylglucosamine-beta-4-(phosphate-6-)mannose), a carbohydrate structure present in alpha-dystroglycan (DAG1) (By similarity). This constitutes the first step in the formation of the ribitol 5-phosphate tandem repeat which links the phosphorylated O-mannosyl trisaccharide to the ligand binding moiety composed of repeats of 3-xylosyl-alpha-1,3-glucuronic acid-beta-1 (By similarity). May interact with and reinforce a large complex encompassing the outside and inside of muscle membranes. Could be involved in brain development (By similarity). 3-O-[beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-(O-6-P-alpha-D-Man)]-Thr-[protein] + CDP-L-ribitol = 3-O-[Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-(O-6-P-alpha-D-Man)]-Thr-[protein] + CMP + H(+) Protein modification; protein glycosylation. Forms a complex composed of FKTN/fukutin, FKRP and RXYLT1/TMEM5 (By similarity). Interacts (via transmembrane domain) with POMGNT1; the interaction is direct and is required for normal POMGNT1 location in Golgi membranes (By similarity). In retinal tissue, does not localize with the Golgi apparatus. Expressed in the retina (at protein level). Belongs to the LicD transferase family.