A smartphone-based digital imaging method has been successfully introduced in an undergraduate laboratory class to quantify fluoride ions in water. Students first synthesized the chemosensor (E)-2-(1-(6-nitro-2-oxo-2H-chromen-3-yl)ethylidene)-N-phenylhydrazine-1-carbothioamide (CT) via an eco-friendly and green microwave-assisted protocol and characterized the product using FTIR spectroscopy, HRMS, and NMR spectroscopy. Students are advised to quantify the colorimetric response of a chemosensor toward fluoride ion by a UV-vis spectrophotometer and smartphone with the preinstalled Color Picker Android application to read the output RGB values, simultaneously. The agreement of results from the developed smartphone-based colorimetry protocol with the conventional UV--vis method validated the feasibility of the smartphone as a new analytical tool for versatile, cheap, and prompt analysis of fluoride ions in real samples. Overall, the experiment develops a multidimensional understanding of green chemistry principles and atom economy as well as characterization techniques, data collection, calibration plots, Job's plot, and interpretation of results.