Tris(2-chloroethyl) phosphite is primarily used as a flame retardant in various polymer systems, including polyesters and polyurethanes. It functions by releasing chlorine radicals during combustion, which interfere with the fire's chemical reactions, thereby reducing flammability. Additionally, it serves as an intermediate in the synthesis of organophosphorus compounds, which are essential in the production of pesticides and plasticizers. Its application is also seen in the stabilization of certain polymers, where it helps to prevent degradation caused by heat or light exposure.