A new cationic clathrate I Si46-xPxTey (6.6(1) <= y <= 7.5(1), x <= 2y at 1375 K) was synthesized from the elements and characterized by X-ray powder diffraction, thermal analysis, scanning electron microscopy, wavelength dispersive X-ray spectroscopy (WDXS), neutron powder diffraction, and P-31 NMR spectroscopy. The thermal behaviors of the magnetic susceptibility and resistivity were investigated as well. Si46-xPxTey reveals a wide homogeneity range due to the presence of vacancies in the tellurium guest positions inside the smaller cage of the clathrate I structure. The vacancy ordering in the structure of Si46-xPxTey causes the change of space group from Pm3n (ideal clathrate I) to Pm3 accompanied by the redistribution of P and Si atoms over different framework positions. Neutron powder diffraction confirmed that P atoms preferably form a cage around the vacancy-containing tellurium guest position. Additionally, P-31 NMR spin-spin relaxation experiments revealed the presence of sites with different coordination of phosphorus atoms. Precise determination of the composition Of Si46-xPxTey by WDXS showed slight but noticeable deviation (x <= 2y) of phosphorus content from the Zintl counting scheme (x = 2y). The compound is diamagnetic while resistivity measurements show activated behavior or that of heavily doped semiconductors. Thermal analysis revealed high stability of the investigated clathrate: Si46-xPxTey melts incongruently at similar to 1460 K in vacuum and is stable in air against oxidation up to 1295 K.