Recovery of ionic liquids (IL) is necessary and urgent because of increasing production costs and potential environmental pollution. Dipolar aprotic solvents (dimethyl sulfoxide, DMSO; N,N-dimethylformamide, DMF; and N,N-dimethylacetamide, DMCA) and polar protic solvents (methanol, ethanol, and n-butanol) were used as cosolvents and antisolvents, respectively. These compounds have crucial effects on the separation and purification of ILs. We determined the effect of different polar solvents on the formation of aqueous biphasic systems (ABSs) using K3PO4 to control the hydrophobicity of 1-alkyl-3-methylimidazolium chloride ([C(n)mim]Cl). Phase equilibria of the ABSs comprising IL + K3PO4 + water in the presence of the polar solvents were obtained at 298 K and at atmospheric pressure. In general, the IL aptitude that induced the formation of ABS in the presence of the polar solvents increased with decreasing hydrogen bond basicity and polarizability of the polar solvents in the following order: none < methanol < ethanol approximate to DMSO < n-butanol approximate to DMF < DMCA. Densities, pH value, conductivities, and surface tensions of both aqueous phases were experimentally measured.