This study evaluated the effects of phosphorus (P) sources (mineral, animal, or plant-based) and phytase supplementation levels (0, 500, or 2500 FTU/kg) on broiler growth performance, nutrient digestibility, bone development, carcass traits, and meat quality using a 3 × 3 factorial design. A total of 1800 male Cobb 500 broilers were reared for 35 days, fed identical basal diets varying only in P source and phytase dose. Significant interactions were observed between P source and phytase level for growth performance, tibia mineralisation, intestinal morphology, and meat quality. High phytase dose (2500 FTU/kg) in plant-based P diets fully restored body weight gain and feed efficiency to the level of mineral P diets, and markedly improved tibia strength, bone mineral content, and intestinal villus height. Carcass traits also responded to phytase supplementation, particularly leg and wing yields. In the absence of phytase, plant-based P diets resulted in the poorest outcomes for growth, nutrient utilisation, bone quality, and meat traits, while mineral and animal P sources produced comparable results. Phytase supplementation reduced drip and cooking losses, though the impact on other traits was less pronounced. For all P sources, phytase improved phosphorus and calcium digestibility, intestinal morphology, and protein status. These findings demonstrate that phytase superdosing effectively mitigate the nutritional limitations of high-phytate plant ingredients, allowing increased inclusion of alternative feedstuffs such as rice bran while reducing dependence on inorganic phosphate without affecting performance or product quality.