A new method of determining the solid point and flow point of crude oil and petroleum products, crystallization/melting of waxes in petroleum products, and the Phazaphot instrument for implementing the method are described. The method consists of recording the intensity of light mirror-reflected from the surface of the sample during structural transitions when the temperature changes. The new principle of measurements allowed significantly simplifying implementation of the method, making the determinations faster, and expanding the range of objects investigated and problems solved.