At school they told me — I was in my early teens — that elemetary phosphorus comes in two principal varieties (actually, four), white and red. White phosphorus is poisonous and inflammable; the red modification is relatively harmless and inert. White phosphorus fluoresces in the dark (whether it was used in bedside alarm clocks, I am not sure). Red phosphorus makes safe matches possible.
Ordinary phosphorus is a waxy white solid; when pure it is colorless and transparent… It takes fire spontaneously in air, burning to the pentoxide. It is very poisonous, 50 mg constituting an approximate fatal dose… White phosphorus should be kept under water, as it is dangerously reactive in air, and it should be handled with forceps, as contact with the skin may cause severe burns.
There’s more here. If this nasty stuff is used in combat, what is it but a chemical weapon?