Ethyldiphenylphosphine oxide is primarily used as an intermediate in organic synthesis, particularly in the production of pharmaceuticals and agrochemicals. It plays a role in the development of ligands for catalytic processes, enhancing the efficiency of metal-catalyzed reactions. Additionally, it is utilized in the preparation of flame retardants, contributing to the safety of various materials. Its application extends to research and development, where it aids in the study of phosphorus-containing compounds and their reactivity.