Phosphorylation and dephosphorylation are two types of enzyme catalyzing reactions that involve phosphate groups. Both are essentially counterparts of each other. 

In the phosphorylation reaction, a phosphate group is added to a molecule. The reaction is catalyzed by the enzyme protein kinase. 

In the dephosphorylation reaction, a phosphate group is removed from a molecule. The reaction is catalyzed by the enzyme phosphatase.