The use of serum albumins (SA) in model systems in the study of the biological activity of chemical compounds and nanomaterials, as well as the physicochemical properties, in particular, phase properties of biological fluids, including the nucleoplasm and cytoplasm of living cells, requires a deeper understanding of the relationship of conformational (structural-dynamic) states of protein molecules with phase states of protein dispersions in a wide range of temperatures and compositions. The joint plotting and analysis of the protein stability curve and phase diagrams of protein solutions commonly used in the study of this relationship are significantly complicated by this protein’s elevated tendency to aggregate. In this paper, an experimental-theoretical approach, based on the application of the electron spin resonance (ESR) of spin labels (maleimido-TEMPO and dichlortriasine-TEMPO spin labels) covalently bound to the protein and sensitive to changes in both the structural-dynamic state of protein molecules and the phase state of protein dispersions, is proposed for studying this relationship. Data on the mobility characteristics of the spin labels (correlation times, state functions, equilibrium constants), indicating the state of intra- and intermolecular interactions of SA molecules, are presented. Transitions in temperature dependences of these characteristics on the temperature and concentration of NaCl, CaCl2, (NH4)2SO4, sucrose, polyethylene glycol, and heavy water have been shown to reflect the interconversions of protein conformers and their aggregates as well as liquid-liquid phase transitions, including those of a reentrant type. Based on the results, a phase diagram of the SA dispersion describing liquid-liquid phase transitions in the temperature range of cold and thermal denaturation and taking into account the role of native protein conformers, their aggregates and transitions between them in the physiological interval has been proposed.