Ag-doped Na–Al phosphate glasses have been used in commercial personal dosimeters for X-rays, γ-rays, and β-rays owing to their radio-photoluminescence (RPL) properties. The RPL behavior in this material when irradiated with high-linear-energy-transfer (LET) radiation has been investigated; however, there are unclear points such as LET quenching. In this study, the proton (3.14 MeV, 22.1 keV/μm) dose dependence of the RPL properties of Ag-doped Na–Al phosphate glasses was investigated as a first step to elucidate the RPL mechanism under high-LET exposure. The optical absorption spectra suggested the formation of Ag0, Ag2+, Ag32+, and the phosphorous–oxygen hole center (POHC) by proton irradiation. In the photoluminescence spectra with an excitation wavelength of 310 nm, broad emission peaking at 650 nm corresponding to Ag2+ and Ag2+ was observed after proton irradiation. Furthermore, the formation of Ag2+, Ag2+, POHC, and peroxy-radical by proton irradiation was revealed in the electron spin resonance spectra. Interestingly, the peroxy-radical signal in Ag-doped phosphate glasses has not been observed in previous studies where the glasses were irradiated with high doses of low-LET radiation, and it is possible that the peroxy-radical is formed only when the glasses are irradiated with high-LET radiation.