Phase diagrams and liquid-liquid equilibrium (LLE) data of the aqueous systems polyethylene glycol 6000 (PEG(6000))-ammonium dihydrogen phosphate and aqueous PEG(6000)-diammonium hydrogen phosphate have been determined experimentally at 298.15, 308.15 and 318.15 K. Furthermore, the osmotic virial equation was used to correlate the phase behavior of these systems. Good agreement was obtained with the experimental data. Finally, the effect of temperature and the type of salt on the LLE are discussed.