A dry, water-soluble, substituted phenoxy and/or benzoic acid herbicide is prepared by grinding and dry blending the herbicide in acid form with anhydrous trisodium phosphate or tripotassium phosphate which functions as a solid solubilization medium. From about 0.6 mole to about 16.9 moles of the medium is provided for each mole of active herbicidal agent in the initially dry blended mixture. Herbicidal agents are selected from the group consisting of 2,4-D, 2,4-DB, MCPP, MCPA, dichlorprop, dicamba, and chloramben.