According to Wikipedia, USA signed part of "Convention on Certain Conventional Weapons" which bans white phosphorus in incendiary weapons in 2009 under Obama administration.
I think the problem is that it's still one of the most effective smokescreen generating compounds out there, so militaries are hesitant to ban it entirely and not have it available for that use.
But, just because it's not marked 'incendiary' on the side of the munition doesn't mean it can be used (both purposefully or accidentally) to horrible effect on people.
But, just because it's not marked 'incendiary' on the side of the munition doesn't mean it can be used (both purposefully or accidentally) to horrible effect on people.