yeah, not sure if that was clear... with too little oxygen the phosphorus may form a dangerous amount of phosphine gas which causes lung failure and can explode easily.

this is what causes bog fires, also, and it doesn't even really take that much heat to do it, but at a certain temperature phosphine just catches fire, this is how safety matches work (the red stuff on the side of the box is partly a form of phosphorus called red phosphorus and the match head contains a friction sensitive oxidiser called potassium perchlorate, so when you rub the two together, the phosphine ignites and kicks off the perchlorate which then lights your match