O-phospho-L-seryl-[3-methyl-2-oxobutanoate dehydrogenase] + H2O = L-seryl-[3-methyl-2-oxobutanoate dehydrogenase] + phosphate
o-phospho-l-seryl-[3-methyl-2-oxobutanoate dehydrogenase] + h2o = l-seryl-[3-methyl-2-oxobutanoate dehydrogenase] + phosphate