Nowadays, there are a variety of different indoor positioning systems employing diverse techniques. On promising approach is Frequency Modulated Continuous Wave- (FMCW) radar, where in addition to several custom approaches, there already exist commercial ICs. Within this work, we are targeting the extension of these systems towards integrating phase measurements with the ultimate goal to improve accuracy. Initially, we present the underlying math for different hardware settings. Subsequently, we focus on our custom FMCW-radar system and analyse the prerequisites for an integration. It becomes clear that already moderate synchronization jitter of 15 μs together with frequency deviations caused by an excellent 20 MHz crystal exhibiting 3 ppm influences operability. We describe our experiments and highlight modifications to establish the principle on the given hardware. Ultimately, this paper contains many lessons learned to simplify the development of similar systems.