Reversible covalent modification controls the direction of glycogen metabolism. Protein kinase A adds a phosphate group; protein phosphatase-1 removes it. The rule for the storage pathway is simple: the enzyme that builds glycogen is turned on when the phosphate is removed.
$\text{Glycogen synthase}_{\text{(dephospho)}} \xrightarrow{\text{active}} \text{glycogen synthesis}$
This matches the fed state, where insulin activates phosphatases. Glycogen phosphorylase behaves oppositely - it needs the phosphate (phosphorylated form) to break glycogen down, which is the fasting/glucagon response. For the bifunctional liver enzyme, dephosphorylation activates the PFK-2 (kinase) activity to drive glycolysis, while phosphorylation favours the bisphosphatase. Thus among the classic storage enzymes, the one switched ON by dephosphorylation is glycogen synthase.
\[\boxed{\text{Glycogen synthase}}\]