Upon ionization of the P4S3I2 molecule with Ag[Al(OR)4], a highly reactive sulfonium cation P4S3I+ is generated (NMR simulated and assigned). At -80 °C this cation reacts with additional P4S3I2 to give either an iodophosphonium P4S3I3+ cation (NMR simulated and assigned) and P4S3 or to give several isomers of a metastable compound that is probably P8S3I3+. This mixture decomposes at 0 °C to give only three isomers of the spirocyclic P7S6I2+ cage cation (31P NMR simulated and assigned, X-ray of one isomer, IR assigned). The oxidation of the [Ag(P4S3)2]+ complex by I2 also resulted in the formation of P7S6I2+, but with more by-products. The spirocyclic 15-atom cage of P7S6I2+ has no precedent and contains the first phosphonium center bonded only to P and S atoms. This structural element gives the first experimental clue as to how formal charge-bearing elements in the still unknown class of binary P-Ch (Ch = chalcogen) or homopolyatomic P cations may be constructed.