Potassium phenyl sulfate is primarily used in biochemical research as a substrate for studying enzyme activity, particularly sulfatases. These enzymes are involved in the hydrolysis of sulfate esters, and the compound helps in understanding their mechanism and kinetics. It is also employed in the development of assays to detect sulfatase activity in various biological samples, aiding in the diagnosis of certain metabolic disorders. Additionally, it serves as a reference standard in analytical chemistry for the quantification of phenyl sulfate derivatives in complex mixtures. Its applications extend to the synthesis of organic compounds where it acts as a sulfate donor in chemical reactions.