Catalyzes the reversible phosphorolysis of beta-(1->2)-D-glucans. The minimum length of the substrate for the phosphorolytic reaction is 3 D-glucose units. [(1->2)-beta-D-glucosyl](n) + phosphate = [(1->2)-beta-D-glucosyl](n-1) + alpha-D-glucose 1-phosphate kcat is 97 sec(-1) for (beta-(1->2)-D-glucans) x 2 units in the synthetic reaction. kcat is 110 sec(-1) for (beta-(1->2)-D-glucans) x 3 units in the synthetic reaction. kcat is 90 sec(-1) for (beta-(1->2)-D-glucans) x 4 units in the synthetic reaction. kcat is 43 sec(-1) for alpha-D-glucose 1-phosphate in the synthetic reaction. kcat is 19 sec(-1) for (beta-(1->2)-D-glucans) x 3 units in the phosphorolytic reaction. kcat is 30 sec(-1) for (beta-(1->2)-D-glucans) x 4 units in the phosphorolytic reaction. kcat is 31 sec(-1) for (beta-(1->2)-D-glucans) x 5 units in the phosphorolytic reaction. Optimum pH is 7.5-8.0. Optimum temperature is 37-45 degrees Celsius. Monomer. Belongs to the glycosyl hydrolase 94 family.