The study of the phase formation of phosphates in the solutions simulating the normal inorganic composition of human urine was carried out by the precipitation method. All calcium and magnesium phosphates typical for the kidney stones were synthesized: brushite, octacalcium phosphate, hydroxyapatite, struvite and Mg-whitlockite. The regularities of the calcium and magnesium phosphates formation in the crystallization medium of variable composition were found out. The borders of the crystallization areas of the synthesized phases were determined in the axes «initial pH value—main components’ concentration». In general, phosphates crystallization areas are defined by the starting concentrations of the main components, pH value of the crystallization medium and by the presence of the additional ions in the solution. It was shown that crystallization of any calcium phosphate leads to the significant decreasing of the pH value of the crystallization medium. Adding of the inorganic components typical for the human urine into the Ca–PO₄ system leads to the moving of the crystallization area borders of the calcium phosphates (brushite, octacalcium phosphate, apatite). Crystallization doesn’t occur in the areas that are characterized by the composition and pH typical for the normal human urine. Increasing amount of the precursors or pH values leads to the start of the phosphate crystallization.