Interetingly enough they are not.
They are considered conventional weapons.
VX Gas (really nasty ****) (This stuff is so nasty its never been used)
Phosphorus is actually present in the human body.
Phosphorus is also an essential ingredient of all cell protoplasm, nervous tissue, and bones.
It's generally used in making many things such as:
In recent years, concentrated phosphoric acids, which may contain as much as 70% to 75% P2O5 content, have become of great importance to agriculture and farm production. World-wide demand for fertilizers has caused record phosphate production. Phosphates are used in the production of special glasses, such as those used for sodium lamps.
Bone-ash --calcium phosphate-- is used to create fine chinaware and to produce mono-calcium phosphate, used in baking powder.
Phosphorus is also important in the production of steels, phosphor bronze, and many other products. Trisodium phosphate is important as a cleaning agent, as a water softener, and for preventing boiler scale and corrosion of pipes and boiler tubes.
Full Article on this element: Phosphorus
Admitedly, Phosphorus is very poisonous but can be handled safely.
White phosphorus weapons are controversial today because of their potential use against civilians. While the Chemical Weapons Convention does not designate WP as a chemical weapon, various unofficial groups consider it to be one. In recent years, the United States, Israel, Russia, and Argentina have used white phosphorus in combat.
Full Article: White phosphorus: Definition from Answers.com