One of the sources that these reports have been using is a single paragraph in the Mar-Apr '05 issue of Field Artillery magazine:

TF 2-2 IN FSE AAR: Indirect Fires in the Battle for Fallujah
White Phosphorous. WP proved to be an effective and versatile munition. We used it for screening missions at two breeches and, later in the fight, as a potent psychological weapon against the insurgents in trench lines and spider holes when we could not get effects on them with HE. We fired “shake and bake” missions at the insurgents, using WP to flush them out and HE to take them out.