Phenylphosphinic acid (PPA), methylphenylphosphinic acid (MPPA), hexachlorocyclotriphosphazene (HCCP), and hexaphenoxycyclotriphosphazene (HPCCP) were prepared and characterized by elemental analysis, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. Using a static analytical method, the solubilities of PPA, MPPA, HCCP, and HPCCP were measured in ten solvents and correlated with an empirical equation. The calculated results showed good agreement with the experimental data. Furthermore, using the Scatchard−Hildebrand model, activity coefficients have also been calculated and compared with the experimental values. The partial molar excess enthalpies at infinite dilution were also predicted.