Beam-forming techniques using phased arrays are one of the most promising solutions for the practical imple- mentation of future high-data-rate point-to-point communication protocols. The functionality of phased arrays is based on the use of phase shifters that should provide an accurate and controllable phase difference between the different paths of the array. However, the integration of phase shifters in current nanometric technologies is prone to imperfections that may affect the intended phase shift and degrade the performance of the antenna array. This requires extensive testing and calibration and represents a bottleneck in the production line of these system. In this work, we propose a simple Oscillation-Based Test technique that may be suitable for Built-In Self-Test applications of phase shifters. The technique is demonstrated on a Reflection-Type Phase Shifter implemented in a 55 nm BiCMOS technology. Elec- tromagnetic and electrical simulation results show the feasibility of the proposed technique.