This paper explores the performance of object localization using chipless tags. We show that it is possible to localize a tag (or an object attached to it) by measuring the phase offset between a known position and the position to estimate. This method provides better accuracy compared to classical ones based on received signal strength indicator (RSSI) or round-trip time of flight. We show that submillimeter precision for distance measurement and an error of less than 4 mm for localization can be achieved. These results point the way toward new kinds of sensors and user interfaces using chipless tags which can be contactless and 3D. This new possibility is in addition to the identification functionality which is inherent to the use of chipless tags.