Actually not quite correct. Here is the Protocol for your pleasure:
Please note the bold and underlined portions. White Phosphorus used as a smoke/screening agent is most certainly allowed by the protocol even though it may have secondary burning effects due to the nature of WP. In Fallujah, the rounds used by the US Military were designed solely for smoke and screening purposes and thus conformed to the Protocol even though the USA is not a signatory to it.
Also please note the complete lack of mentioning White Phosporus directly in the protocol. It is meant to cover any and all types of incendiary devices designed for use against people - like the old Napalm bombs of the Vietnam Era. Thats not how White Phosphorus is used.
Oh..and btw, Isreal is not a signatory of Protocol III either.
http://www.icrc.org/eng/party_ccw
Class dismissed.