The red-emitting Sr[LiAl3N4]:Eu2+ (SLA) phosphor was synthesized under flowing N-2 gas. A thin organosilica layer (about 5-10 nm) was coated on the surface of SLA phosphors by a very simple method, which transformed the phosphor surface from hydrophilicity to hydrophobicity. The contact angle of water droplets on the surface of the packed SLA phosphors was more than 140 degrees. Compared with the unmodified sample, the modified SLA phosphors could keep at a high emission intensity for more than twice the time under an extremely high moisture level (at relative humidity of 100%, 85 degrees C). The hydrophobic modification could also improve the uniform dispersion of phosphors during assembly process of white LED.