WP suspended inside a flammable liquid is a thing that has been done, both by state and non state actors.

On 29 July 1940, manufacturers Albright and Wilson of Oldbury demonstrated to the Royal Air Force how their white phosphorus could be used to ignite incendiary bombs. The demonstration involved throwing glass bottles containing a mixture of petrol (gasoline) and phosphorus at pieces of wood and into a hut. Upon breaking, the phosphorus was exposed to the air and spontaneously ignited; the petrol also burned, resulting in a fierce fire.