The transfer of a Ph2P+-moiety provided by Ph2PCl and chloronium-addition with PCl5 or PhICl2 to the cyclo-phosphanes (t-BuP)n (n = 3 (4), 4 (5)) were investigated. The reactions strongly depend on the presence of GaCl3 or Me3SiOTf as a halide abstracting reagent. The reaction of 4 with Ph2PCl and GaCl3 quantitatively yields cation [Ph2P(t-BuP)3]+ (6+) as a GaCl4–-salt. Using Me3SiOTf as a halide abstracting reagent leads to the ring expansion of (t-BuP)3 (4) to tetrameric (t-BuP)4 (5) and cation 6+ is only formed as a minor product. Chloronium addition employing the PCl5/GaCl3 or PhICl2/Me3SiOTf systems as Cl+-sources to 4 gives complex reaction mixtures. In contrast, the Cl+-addition to 5 gives cation [Cl(t-BuP)4]+ (8+) quantitatively when the system PCl5/GaCl3 is used. Utilising PhICl2 in the presence of Me3SiOTf gives t-BuPCl2 as the main product.