The aim of wheat cultivation is to achieve high grain yield while ensuring food quality and adopting environmentally sustainable practices, including the use of alternative phosphorus fertilizers. Grain size and shape are critical parameters influencing technological and industrial processing. This study aimed to evaluate the effects of two phosphorus fertilizers—struvite and superphosphate—on the yield and geometric traits of two winter wheat (Triticum aestivum L.) cultivars, Activus and Chevignon, under field conditions. The results demonstrated significant differences between cultivars in grain physical characteristics, including grain density and the proportion of grains >2.5 mm, with Activus exhibiting more favorable traits. Grain width, thickness, and dimension ratios varied significantly depending on both cultivar and fertilization method. Activus showed higher values of thickness and kernel width index (Kw) under superphosphate fertilization. Conversely, Chevignon exhibited greater grain width, particularly under superphosphate treatment. Cultivar type significantly influenced key geometric parameters including arithmetic (Da), geometric (Dg), and equivalent (Dp) mean diameters, aspect ratio (Ra), and ellipsoid shape factor (Fz), with higher values observed for Chevignon. Phosphorus fertilization, particularly with superphosphate, positively affected Dg, Dp, Φ, and Ra, suggesting its greater efficacy in enhancing grain morphology.