Is the initiating enzyme for colanic acid (CA) synthesis. Catalyzes the transfer of the glucose-1-phosphate moiety from UDP-Glc onto the carrier lipid undecaprenyl phosphate (C55-P), forming a phosphoanhydride bond yielding to glucosyl-pyrophosphoryl-undecaprenol (Glc-PP-C55). Also possesses a weak galactose-1-P transferase activity. di-trans,octa-cis-undecaprenyl phosphate + UDP-alpha-D-glucose = alpha-D-glucosyl di-trans,octa-cis-undecaprenyl diphosphate + UMP Exopolysaccharide biosynthesis; colanic acid biosynthesis. Cells lacking this gene show a non-mucoid phenotype. Complements holdfast synthesis in the C.crescentus mutant lacking hfsE, pssY and pssZ genes. Can also partially complement the O-antigen defect in the S.typhimurium wbaP deletion strain (PubMed:22408159). Belongs to the bacterial sugar transferase family.