Cathodoluminescence spectra of Ca codoped (La,Ce)Al(Si6-zAlz)(N10-zOz) (z similar to 1) (termed JEM phase) phosphors were analyzed microscopically. The as-prepared samples consisted of a major JEM phase and a small amount of -sialon and/or -sialon depending on the Ca concentration. A microscale distribution of three different emission spectra was clearly observed on one phosphor particle, which was originated from the blue-emitting JEM:Ce (430nm), -sialon:Ce (435nm) and Ca--sialon:Ce (475nm), respectively. The volume ratio of the three phases thus led to changes in the bandwidth and the maximum position of the emission spectrum, and the redshift of CL spectra with increasing Ca concentration was dominantly attributed to the enhanced emission from Ca--sialon. The microanalysis of phosphor particles with the aid of cathodoluminescence spectroscopy indicated a similar result of the phase assembly that was identified by the powder X-ray diffraction.