Mediates the conversion of kanamycin B into 2'-dehydrokanamycin A during the transformation of kanamycin B to kanamycin A. 2-oxoglutarate + kanamycin B + O2 = 2'-dehydrokanamycin A + CO2 + NH4(+) + succinate Antibiotic biosynthesis; kanamycin biosynthesis. Belongs to the PhyH family.