There's no doubt that white phosphorus is being used in Iraq. From Infantry Magazine:
 http://www.findarticles.com/p/articles/mi_m0IAV/is_3_93/ai_n6366546

"The 60mm mortars from Alpha Company, 1-508th Infantry, were tasked to provide immediate indirect fire support onto known and suspected targets. Upon reaching their planned mortar firing point, the section immediately dismounted their HMMWV (high-mobility multipurpose wheeled vehicle) and conducted an emergency occupation. The section immediately received a call for fire from their forward observers. Within 60 seconds of occupation, the section was placing accurate high explosive (HE) and white phosphorus (WP) rounds onto and in the vicinity of the Iraqi observations posts [...]"

"The Iraqis in one observation post attempted to flee but were fixed with white phosphorus fires. As they attempted to flee again, white phosphorus rounds impacted the vehicle and set it on fire. The section continued to fire a mix of high explosive and white phosphorus rounds into the objective area. The section fired more than 80 rounds in support of the mission. Upon receiving the order to displace and reorganize for the movement back to the battalion assembly area, the 105s, 120s and 60s quickly broke their systems down and moved out. The rifle companies continued to provide suppressive fire onto the objectives."

The question is not whether the United States is technically in violation of any treaty obligations. It is not. The issue here is the use of a weapon that is further eroding the US's moral standing in this war. We supposedly invaded because of Saddam's use of chemical weapons and torture. Well, now we torture and use WP. And if it walks like a duck, and quacks like a duck:
 http://www.nsc.org/library/chemical/phsphor.htm

"White phosphorus is a poison which can be absorbed through skin contact, ingestion, or breathing. If its combustion occurs in a confined space, white phosphorus will remove the oxygen from the air and render the air unfit to support life. Long-term absorption, particularly through the lungs and the gastrointestinal tract, can cause chronic poisoning, which leads to weakness, anemia, loss of appetite, gastrointestinal weakness, and pallor."

"Eating or drinking less than one teaspoon of white phosphorus can cause vomiting; stomach cramps; liver, heart or kidney damage; drowsiness; and even death. Being burned with white phosphorus can cause heart, liver, and kidney damage. Breathing white phosphorus may damage lungs and throat."

"White phosphorus can cause changes in the long bones; seriously affected bones may become brittle, leading to spontaneous fractures. White phosphorus is especially hazardous to the eyes and can severely damage them."

"High concentrations of the vapors evolved by burning white phosphorus are irritating to the nose, throat, lungs, skin, eyes, and mucus membranes.
Breathing white phosphorus can cause coughing and the development of a condition known as phossy jaw -- poor wound healing in the mouth and a breakdown of the jaw bone. The most common symptom of exposure to white phosphorus is necrosis of the jaw."

"Exposure to white phosphorus can also cause nausea, jaundice, anemia, cachexia, dental pain, and excess saliva."

And we know for a fact that U.S. forces used WP in the attack on Fallujah, with predictable results for the city's innocent civilian population. (Including the babies):
 http://www.dailykos.com/storyonly/2005/11/9/174518/797

WP has legit military applications for battlefield illumination and artillery spotting. But from a moral standpoint, its use as an anti-personnel munition is, by all measures, unconscionable. That is, unless we're willing to abandon outrage over Saddam's use of chemical weapons.