A three-phase induction motor (IM) is one of the most widely used motors in various industrial and commercial applications due to its reliability, robustness, simplicity, low maintenance...etc. Despite its many features, it is exposed to many faults that affect its performance and may cause damage and burning of its coils. Among these faults is opining of phase during its operation which leads to an increase in the temperature of its windings. In this research, a highly efficient algorithm is designed to detect and classify 19 different types of open phase faults. This algorithm is based on rules or conditions derived from simulating the different types of open phase faults in three motor modes (steady-state, transient, and standstill modes). The proposed algorithm uses the per-unit values of the phase voltages, line currents and speed as well of the motor and thus can be applied to different motors. The proposed algorithm has been designed and tested using the simulink window in MATLAB software. All test results proved that the proposed algorithm works very efficiently and is characterized by its speed and high accuracy in detecting these faults. Therefore, it can be used and integrated within the main protection system of a 3-phase IM to detect and classify the various open phase faults.