We present a passive digital-to-phase converter with sub-degree phase precision for phased array frontends. The phase tuning approach is based on manipulating the electromagnetic properties of an artificially constructed transmission line. By simultaneously controlling dispersion, characteristic impedance, and loss across the structure, the phase shifter minimizes phase imprecisions while ensuring a flat amplitude response across different phase settings. The chip prototype is fabricated in a 130nm SiGe BiCMOS process, occupies an area of 0.18mm2, and consumes no power. The insertion loss is -9.3 dB ± 0.25 dB at 28 GHz. The phase control operates with 4.75 degree steps while maintaining an RMS phase error of 0.6 degrees across multiple chips and temperatures, demonstrating the best phase and amplitude accuracy when compared to state-of-the-art integrated microwave and mm-wave phase shifters.