metal‐free hydrophosphinylation of unactivatedalkenes with ethyl and butyl phosphinates is described. The reaction works with a low catalyst loading of 9‐mesityl‐10‐methylacridinium perchlorate (Fukuzumi photocatalyst, 0.5 mol %) in the presence of diphenyliodonium triflate as oxidant. The reaction proceeds smoothly and covers a broad scope of substrates. Detailed mechanistic investigations, including EPR