Abstract Background: Over the years, various fixation methods have been developed for managing unstable proximal humerus fractures (PHFs), including conservative and surgical approaches like tension band wiring, suture fixation, intramedullary nailing, hemiarthroplasty, fixed-angled locking plates, and proximal humerus internal locking system (PHILOS) plating. Each method claims superior effectiveness as a fixation device. Aims: The study evaluated the functional outcome of the PHILOS in different parts of the PHF using the Constant–Murley score (CMS), which measures post-operative pain, daily activity ability, limb range of motion (ROM), and strength. Materials and Methods: A prospective observational study of 50 participants aged 16 years and above at Rajasthan Hospitals in Ahmedabad, conducted from July 2020 to July 2022, examined the use of the PHILOS for PHF treatment. Results: The results revealed that two-part fractures had a significantly higher mean CMS (72.4 ± 10.8) compared with three-part (60.8 ± 8.1) and four-part (59.3 ± 5.3) fractures. The P value of 0.0003 indicated that the difference in CMS score between two and three or four parts of PHF after fixing them with PHILOS was statistically significant. Conclusion: The study concludes that using a locking plate for PHFs consistently leads to positive clinical and functional outcomes, including improved CMS, daily living activities, and ROM.