The bond nature of a (NaPO₃)_n-containing basic refractory material was investigated versus the heating temperature. At room temperature, the raw binder (NaPO₃)n was shown to contain an average of 15 units per chain leading to a binding gel formation when the refractory material is added with water. As the raw mix temperature increases, the gel converts into a mixed sodium calcium phosphate phase stable in the temperature range [500-1000°C]. Beyond 1100°C, the mixed sodium calcium phosphate reacts with intergranular silicate phases. It transforms, then, into a mixed sodium calcium silicophosphate solid solution. This high temperature silicophosphate bond exhibits a lower decomposition kinetic than that of the mixed sodium calcium phosphate which decomposes, at low temperature, into β-NaCaPO₄ and Ca₅(PO₄)₃OH.