Chromium(VI) is proved to be highly carcinogenic and mutagenic, thus sensitive and rapid sensors for monitoring Cr(VI) are in urgent demand. In this work, a facile fluorescent assay for the sensitive and selective detection of Cr(VI) was proposed based on static quenching combined with inner filter effect (IFE) using phosphate functionalized carbon dots (PCDs) as nanoprobes. A good linear quenching was observed in the range of 1.0–400 μM with a detection limit of 0.24 μM (σ/S = 3) under the optimized conditions. The nanoprobe was employed for detecting Cr(VI) in real water samples including river water and tap water with satisfactory recovery. Moreover, with the addition of Cr(VI), the color changes of PCDs can be easily observed by the naked eye under a UV lamp. Based on this, Cr(VI) test papers were fabricated for spot quick detection of Cr(VI).