The reaction of phenylphosphonic dichloride with bisphenol A (BA) by inverse phase transfer catalysis method was investigated. The design of experiments method was applied to establish the correlation between the simultaneous influence of the parameters (alkaline medium, reaction temperature, reagents molar ratio, and stirring speed) on yield and inherent viscosity, as well as for identifying the best reaction conditions. This method allows the simultaneous variation of control factors, thus decreasing the number of experiments in the polyphosphate synthesis. The process control factors used in this study were reagents' molar ratio, base concentration, and reaction temperature. The experimental results using 20 and 14 process runs, lead to an optimal synthesis procedure. The optimal values for yield and viscosity were obtained at molar ratio = 1, base concentration = 1.1 M, and reaction temperature = -12 degrees C and have been experimentally verified with a series of four runs.