Just an observation, but the pictures of the use of WP all seem to be air bursts, which would suggest its use as a smoke screen, rather than directly anti-personnel.
http://en.wikipedia.org/wiki/White_phosphorus
The emotive phrase 'chemical weapon' is a difficult one - strictly speaking gunpowder/cordite/tnt/napalm are all 'chemical weapons', but not in the way nerve gases, etc are, in that they rely on explosive or incendiary effects, rather than toxicity.