The interactions of phosphate salts like disodium hydrogen phosphate (Na2HPO4) and dipotassium hydrogen phosphate (K2HPO4) with 1-hexyl-3-methylimidazolium chloride ([C(6)mim][Cl]) as a function of temperature have been investigated by combination of volumetric and acoustic measurements. Densities, rho, and speeds of sound, u, for phosphate salts in aqueous solutions of 1-hexyl-3-methylimidazolium chloride have been measured at T = (288.15, 293.15, 298.15, 303.15, 308.15) K and atmospheric pressure. The apparent molar volume, limiting apparent molar volume and standard partial molar volumes of transfer for phosphate salts from water to aqueous 1-hexyl-3-methylimidazolium chloride solutions have been calculated from density data. Apparent molar isentropic compression, limiting apparent molar isentropic compression and standard partial molar isentropic compression of transfer have been calculated from speeds of sound data. The UV absorption studies have also made in this study. The results have been explained in terms of competing patterns of interactions of cosolvent and the solute.