Process to make light olefins, in a combined XTO (organics to olefins)-OCP (olefins cracking process) process, from an oxygen-containing, halogenide-containing or sulphur-containing organic feedstock comprising: contacting said oxygen-containing, halogenide-containing or sulphur-containing organic feedstock in the XTO reactor with a catalyst made of a P-modified zeolite obtained from a crystalline alumosilicate with a Si/AI ratio below 30 at conditions effective to convert at least a portion of the feedstock to form a XTO reactor effluent comprising light olefins, i.e. ethylene and propylene, and a heavy hydrocarbon fraction, i.e. hydrocarbons having 4 carbon atoms or more; separating said light olefins from said heavy hydrocarbon fraction; contacting said heavy hydrocarbon fraction in the OCP reactor with a catalyst made of a P-modified zeolite at conditions effective to convert at least a portion of said heavy hydrocarbon fraction to light olefins; wherein said P-modified zeolite is made by a process comprising in that order: - selecting a zeolite with a Si/AI ratio below 30 among H + or NH 4 + -form of MFI, MEL, FER, MOR, clinoptilolite; - introducing P at conditions effective to introduce advantageously at least 0.05 wt% of P; - separation of the solid from the liquid if any; - an optional washing step or an optional drying step or an optional drying step followed by a washing step; - a calcination step; the catalyst of the XTO and the catalyst of the OCP being the same or different. contacting said oxygen-containing, halogenide-containing or sulphur-containing organic feedstock in the XTO reactor with a catalyst made of a P-modified zeolite obtained from a crystalline alumosilicate with a Si/AI ratio below 30 at conditions effective to convert at least a portion of the feedstock to form a XTO reactor effluent comprising light olefins, i.e. ethylene and propylene, and a heavy hydrocarbon fraction, i.e. hydrocarbons having 4 carbon atoms or more; separating said light olefins from said heavy hydrocarbon fraction; contacting said heavy hydrocarbon fraction in the OCP reactor with a catalyst made of a P-modified zeolite at conditions effective to convert at least a portion of said heavy hydrocarbon fraction to light olefins; wherein said P-modified zeolite is made by a process comprising in that order: - selecting a zeolite with a Si/AI ratio below 30 among H + or NH 4 + -form of MFI, MEL, FER, MOR, clinoptilolite; - introducing P at conditions effective to introduce advantageously at least 0.05 wt% of P; - separation of the solid from the liquid if any; - an optional washing step or an optional drying step or an optional drying step followed by a washing step; - a calcination step; the catalyst of the XTO and the catalyst of the OCP being the same or different. - selecting a zeolite with a Si/AI ratio below 30 among H + or NH 4 + -form of MFI, MEL, FER, MOR, clinoptilolite; - introducing P at conditions effective to introduce advantageously at least 0.05 wt% of P; - separation of the solid from the liquid if any; - an optional washing step or an optional drying step or an optional drying step followed by a washing step; - a calcination step; the catalyst of the XTO and the catalyst of the OCP being the same or different.