This work addresses the effect of different anions in imidazolium-based ionic liquids (ILs) through the formation of aqueous biphasic systems (ABS) using a phosphate buffer solution (KH2PO4/K2HPO4 mixture of salts) aiming at controlling the pH value of the coexisting aqueous phases. Twelve ABS were investigated and the corresponding solubility curves were determined by the cloud point titration method at 298 K. In general, the IL anions aptitude to induce the formation of ABS increases with the decrease of the ability of the ions to form hydration complexes, i.e., with the decrease on the hydrogen-bond basicity of individual fluids. This trend is in close agreement to that observed in ABS with different inorganic salts, showing that the ILs rank is not dependent on the salting-out species used.