A magnetically coupled near-field chipless resistive sensor label, based on measuring phase at a single frequency is presented. The sensor need not determine the exact resonant frequency or quality factor, and offers high sensitivity, accuracy and dynamic range. It is also insensitive to read range variation and orientation. Being a magnetically coupled near-field system, it is fundamentally more robust against clutter compared to propagating wave counterparts. An equivalent circuit analysis in conjunction with circuit simulation and experiments is presented.