Phosphate is essential for plant growth and development. Root architecture alternations induced by phosphate starvation (-Pi), including primary root and lateral root growth, are mediated by iron (Fe). However, whether and how Fe participates in the -Pi-induced root hair growth (RHG) remains unclear. Here, with morphological, proteomic, and pharmacological analysis, we investigate the impacts of Fe on RHG under -Pi and the underlying mechanisms. We found that -Pi-induced RHG was affected by the local Fe availability. Reduced sensitivity to Fe was found in aux1-7, arf10arf16, and phr1 under -Pi, indicating auxin and phosphate starvation-induced responses were required for the Fe-triggered RHG under -Pi. Fe availability was then found to affect the auxin distribution and expression of phosphate starvation-responsive (PSR) genes. Proteomic analysis indicated vesicle trafficking was affected by Fe under -Pi. With the application of brefeldin A, we found the vesicle trafficking was affected by Fe, and root hairs displayed reduced sensitivity to Fe, indicating the vesicle trafficking is critical for Fe-triggered RHG under -Pi. Our data suggested that Fe is involved in RHG under -Pi by integrating the vesicle trafficking, auxin distribution, and PSR. It further enriches the understanding of the interplay between phosphate and iron on RHG.