Phosphates vs Phosphonates
Managed to dig up the following:
Phosphonate compounds containing more than one phosphonate group are effective sequestrants and possess other useful properties such as high water solubility, chemical stability, bleach stabilizing effects, and the ability to prevent precipitation of calcium salts at substoichiometric concentrations.
Phosphates remove hardness, reduces surfactant use, improves emulsification and dispersion, prevents re-deposition, and controls alkalinity.