Phosphorylase showing strict alpha-1,3-regioselectivity and producing 3-O-alpha-D-glucopyranosyl-L-rhamnopyranose. Specific for L-rhamnose as acceptor and beta-D-glucose 1-phosphate as donor. Does not phosphorylate alpha,alpha-trehalose, kojibiose, nigerose, or maltose. 3-O-alpha-D-glucosyl-L-rhamnose + phosphate = beta-D-glucose 1-phosphate + L-rhamnopyranose kcat is 16 sec(-1) with L-rhamnose. kcat is 2.5 sec(-1) with beta-D-glucose 1-phosphate. Optimum pH is 6.5. Monomer. Belongs to the glycosyl hydrolase 65 family.