Abstract: In the domain of sustainable construction, the practice of integrating recycled solid waste into asphalt pavements has emerged as a critical innovation over recent years. This approach not only contributes to environmental sustainability but also enhances the structural stability of pavements. The unique physical and chemical properties of solid waste contribute substantially to improving both the temperature stability and fatigue resistance of asphalt, which are vital for the long-term durability and functionality of asphalt pavements. By enhancing these characteristics, the use of solid waste extends the operational life of asphalt pavements and optimizes the use of recycled materials in construction. This study used phosphogypsum whisker (PSW) as the main material to develop a composite modifier (MPM) for modifying virgin asphalt. The impact of varying levels of modifier on the aging resistance and rheological behavior of asphalt was explored using the rolling thin film oven test (RTFOT) along with various rheological evaluations. Additionally, the role of MPM in modifying asphalt was examined through a series of microscopic examinations. Findings indicated that the advanced composite modification technique significantly enhanced the dispersion of MPSW throughout the asphalt matrix. With MPM dosage below 6%, there was a noticeable improvement in the thermal and mechanical performance of the virgin asphalt, along with increased resistance to rutting, unaffected by aging. This improvement also contributed to an extension of the fatigue life of asphalt within specific strain limits. Furthermore, the physical integration of MPM with the virgin asphalt markedly boosted its thermal stability. A quantitative model analyzing MPM dosage was developed, aiming to serve as a guideline for the integration of PSW into asphalt pavements.