The paper presents the results on modelling high pressure phase behaviour of the systems consisting of refrigerant, trifluoromethane (R23) and 1-phenylpropane. There were used cubic equations of state (GEOS, SRK and PR) coupled with van der Waals mixing rules in a semi-predictive approach (SPA). Based on the experimental VLE isothermal data in the range 300–330 K, binary interaction parameters (BIPs) were optimized, through regression of bubble pressure type. Unique sets of interaction parameters were estimated for each EoS, and used in the SPA to calculate the critical, subcritical and supercritical behaviour of the system. The SPA calculations are comparatively discussed with the available experimental data in the temperature range (250–400) K and pressures up to 12 MPa. The calculations of critical line and of vapour-liquid, liquid-liquid, vapour-liquid-liquid phase equilibria, and of critical endpoints indicate a good modelling capacity of the tested EoSs and an accurate representation of the complex critical and subcritical behaviour of the investigated system.