I don't want to get too into current events, but Israel says it discontinued current use in 2013 of white phosphorus. Whether it still uses them is contentious, but that's not for here. Let's avoid the 20 year rule.

White phosphorus does not violate international law when used correctly.

Chemical weapons are indeed banned under international law. However, white phosphorus is not a chemical weapon. It is an incendiary weapon (maybe). That argument, made here, relates to the fact that both munitions types have clearly defined definitional terms that white phosphorus does not fit as far as banned status. White phosphorus may not even be an incendiary weapon because its main uses are not incendiary, but are for the use of smokescreen (what Israel has said in the past it uses it for). The Chemical Weapons Convention deals with chemical processes affected by the weapon, but white phosphorus doesn't actually operate on chemical processes of the sort it describes.

This view is debated frequently, but others have also articulated it. At any rate, even if it's used, so long as it is used solely as a smokescreen, it violates none of the rules of war, or close to it.

It is that use of it as a smokescreen that makes it valuable in other contexts, and leads to it not falling within the text of treaties. International law rarely bans weapons that have legal uses that are nonlethal in intent, even if they are also misused.

International law is not my specialty, but in either case, white phosphorus is not banned, and that is intentional. The US also has a reservation to the treaty related to using it in areas where civilians may be among military (when it would save more civilians overall to use), though how much legal latitude that gives it...depends who you ask.