Hydrolyzes cellobiose 6'-phosphate into glucose 6-phosphate (Glc6P) and glucose. 6-phospho-beta-D-glucosyl-(1->4)-D-glucose + H2O = D-glucose + D-glucose 6-phosphate Binds 1 NAD(+) per subunit. Binds 1 Mn(2+) ion per subunit. Optimum pH is 8.0. Active from pH 6.5 to 10. Homodimer or homotetramer. Exists in a homodimer/homotetramer equilibrium state in solution. Is a retaining glucosidase as it hydrolyzes glycosidic bond with retention of anomeric configuration. Reaction mechanism includes redox steps involving NAD and stabilization of intermediates by Mn(2+). Belongs to the glycosyl hydrolase 4 family.