A process may include selecting a zeolite, introducing phosphorus (P) to the zeolite, calcining the zeolite and obtaining a P modified zeolite. The process may include contacting an oxygen-containing, halogenide-containing or sulphur-containing organic feedstock in a first reactor with a first catalyst that includes the P-modified zeolite at conditions effective to convert at least a portion of the feedstock to form a first reactor effluent that includes light olefins and a heavy hydrocarbon fraction. The process may include separating the light olefins from the heavy hydrocarbon fraction, and contacting the heavy hydrocarbon fraction in a second reactor with a second catalyst that includes the P-modified zeolite at conditions effective to convert at least a portion of the heavy hydrocarbon fraction to light olefins. The first catalyst and the second catalyst may be the same or different.