The high toxicity of phosgene poses potential threats to public health and safety. In this work, a novel fluorescent probe was designed to detect phosgene using hydroxyl and pyrazole moieties as the recognition sites. The response to phosgene with probe 1 was fast (less than 30 s), highly selective and sensitive with the limit of detection being 4.78 nM in solution. Furthermore, probe 1 was employed to conveniently fabricate paper test strips for efficiently detecting phosgene gas. The limit of detection was obtained as 0.014 ppm by using a smartphone RGB app, revealing that probe 1 has good prospects for sensitively detecting phosgene gas.