In this study, the phase stability of the polycrystalline TMFZ (Ti–12Mo–6Zr–2Fe, wt%) alloy, produced by electron beam melting and thermomechanically processed through swaging, was evaluated by ultrasonic measurements at cryogenic temperatures. XRD and SEM analyses at room temperature confirmed the presence of a major β phase as equiaxial grains and a minor α” phase in the form of acicular structures. Ultrasonic measurements were realized with 10 MHz ultrasonic pulses and the pulse-echo technique in cooling-heating cycles of temperature between room temperature and 150 K. Some anomalies in the ultrasonic attenuation and velocity at cryogenic temperatures were related to the alloy’s phase transitions in the temperature range investigated. The anomaly observed at the lowest temperature investigated was compared with the diagram calculated using the CALPHAD, which predicted the formation of an ω phase (bcc crystalline structure) at low temperatures. This finding also supported some theoretical phase predictions for Ti’s solid solutions. Detection of the α → ω phase transition at cryogenic temperatures in the TMFZ alloy can open new horizons for novel industrial applications, particularly those operating under extreme temperature conditions.