A novel visible-light photoredox-catalyzed phosphinyloxy radical addition/cyclization cascade of arylphosphinic acids or arylphosphonic acid monoesters with alkynes has been developed, which provides an efficient and practical access to various phosphaisocoumarins by using a dual catalytic system containing an acridinium photosensitizer and a cobaloxime proton-reducing catalyst [Co(dmgH)2]PyCl at ambient temperature. This method has advantages of a broad substrate scope, mild condition, as well as no sacrificial oxidant.