A blue-emitting Eu2+-doped Ca3Mg3(PO4)4 phosphor was prepared by the polyethylene glycol assisted sol-gel synthesis method. The prepared phosphor was analyzed by using X-ray diffraction and scanning electron microscopy for the investigation of its structural and morphological features. From the photoluminescence (PL) excitation and emission spectra, it was found that the prepared phosphor emits blue light under ultraviolet and near-ultraviolet excitation. Temperature-dependent PL spectra and PL lifetime decay measurements were also executed for determining the detailed features of the Eu2+ emission in this phosphor. Under 325 nm excitation, the phosphor demonstrated excellent thermal stability with the activation energy for thermal quenching of 0.291 eV. The electron-vibrational interaction in the 5d states of the optimum Eu2+-concentration present in the blue-emitting Ca3Mg3(PO4)4:Eu2+ phosphor was evaluated and discussed by using the spectrum-fitting method.