Leaf angle and curvature are considered important by breeders for increasing plant productivity. We developed a smartphone app (PocketPlant3D) that makes use of the device accelerometer and magnetometer to measure leaf insertion angle and the leaf angles from the insertion to the tip, in turn used to reconstruct the 3D distribution of the angles of photosynthetic tissues. Starting from these angles, PocketPlant3D derives the mean leaf tilt angle (MTA) and the parameters of the Campbell and β leaf angle distributions (LAD), as well as a new leaf curvature indicator. The app was compared with other methods for quantifying precision in measuring leaf insertion angle on maize and sweetcorn (4320 leaf insertion angle measurements) via a ring test. Both precision metrics (repeatability and reproducibility) were similar for the different methods, with the exception of the digital inclinometer, which was the less precise. Concerning the analysis of canopy structure (a total of more than 72,000 angles were measured), PocketPlant3D allowed two genotypes to be discriminated for MTA and, especially, for the parameters of the two LADs and for the curvature indicator, whereas the two genotypes presented similar leaf insertion angles. The completeness of the information collected and the time effectiveness make PocketPlant3D a useful tool for phenotyping activities and ecophysiological studies.