Zykon TheLich said:
IIRC you can temporarily put out WP by submerging it completely in water since it spontaneously combusts in oxygen.
White phosphorous doesn't burn in the conventional sense. Instead, the phosphorous reacts directly with the oxygen in the air to produce a chemical called phosphorus pentoxide. Phosphorous pentoxide, when exposed to water, undergoes hydrolysis, becoming phosphoric acid. This hydrolysis is also highly exothermic.
The use of white phosphorous as a weapon is controversial because although most of the damage will come from heat, it works by exploiting the chemical properties of phosphorous to more effectively penetrate and damage the human body from the inside by using this series of reactions (and also leave long term poisoning, because none of these chemicals are good to have inside you). Because of this, the use of white phosphorous as a weapon straddles the line between conventional incendiaries and chemical warfare, and while it's not entirely clear cut on whether international treaties forbid the use of white phosphorous as an incendiary weapon, the fact that it's impossible to separate the incendiary and chemical effects make it hugely questionable. Because of this, the use of white phosphorous as a weapon is denied by most developed armed forces with the insistence that its use is limited to illumination and smoke generation.
However, this is not actually true. There are numerous recorded instances of white phosphorous being used as an offensive weapon with involvement or support from armed forces which officially deny its use, right up into the present day, seemingly with impunity or even official sanction, both directly against military targets and indiscriminately against civilians. A notable case in point was the battle of Fallujah, where footage emerged of WP being fired from helicopters into civilian areas, as well as civilian casualties burned by it.
That is why it is controversial. It's nothing to do with the inherent properties of white phosphorous, but because it has been used in recent, living memory to conduct organised war crimes, crimes which were officially denied but of which clear evidence exists, by those same military forces who are usually presented in a heroic light within the modern military shooter genre.
Context matters.