A phosphor layer composition, phosphor member, light source device, and projection device are provided that are capable of restraining reflection or scattering at interfaces between phosphor particles and a binder to improve the excitation-light absorption by, and the external quantum efficiency of, the phosphor particles. The present invention, in an aspect thereof, is directed to a phosphor layer composition including: phosphor particles 111 absorbing excitation light and emitting prescribed fluorescence; and a binder 112 composed of a translucent gel containing a metal alkoxide or a mixture of a metal alkoxide and a metal oxide, wherein the phosphor particles 111 are dispersed in the binder 112, and the phosphor particles 111 and the binder 112 differ in refractive index by 0.3 or less.