In this paper, we investigate a coherent imaging system based on Terahertz and mid-infrared (MIR) quantum cascade lasers (QCLs) in terms of phase sensitivity against optical feedback. In the self-mixing scheme, a single QCL acting as oscillator, mixer and detector of infrared radiation, is used for continuous-wave reflection imaging as well as phase profiling. We study the dependence of the phase signature on the optical feedback level and assess the limit for phase signal detection. Index Terms—Quantum cascade laser (QCL), THz imaging, optical feedback interferometry, optical sensing, laser sensors.