Asphalt binder is a fundamental material in pavement construction due to its strong adhesion to mineral aggregates and viscoelastic response, which enables it to sustain diverse traffic and environmental loading conditions. However, its inherent temperature- and time-dependent behavior makes conventional asphalt susceptible to distresses such as rutting at high temperatures and cracking under repeated or low-temperature loading, ultimately degrading pavement performance. Polymer modification, particularly using styrene-butadiene-styrene (SBS), has therefore become a widely adopted approach to enhance binder rheology, elasticity, and durability. Despite extensive research on SBS-modified asphalt, a unified understanding of how polymer structure, dosage, and phase behavior collectively govern binder performance remains limited, especially for systems with high polymer content. This review addresses this gap by systematically differentiating between commonly used SBS-modified binders (2–3 %) and highly modified asphalt (HiMA) systems incorporating elevated SBS contents (7–8 % and above). It critically examines their modification mechanisms, microstructural evolution, phase stability, and aging behavior. Particular emphasis is placed on the phase inversion phenomenon occurring at higher SBS dosages, where the polymer transitions to a continuous phase, forming a well-developed elastic network that significantly enhances rutting and fatigue resistance. However, this structural transformation is also associated with challenges related to blending efficiency, compatibility, workability, and long-term storage stability. The effectiveness of stabilizing strategies, including sulfur, phosphoric acid, nano clays, and graphene-based additives, is discussed in the context of improving network integrity and durability. Unlike earlier descriptive reviews, the present work offers a critical comparison of conventional SBS binders and HiMA systems, highlighting how phase inversion, polymer network formation, and compatibility constraints jointly control performance. The review identifies key unresolved challenges in HiMA production and outlines emerging research directions that integrate microstructural characterization with advanced rheological and additive technologies to support the sustainable implementation of SBS-based asphalt pavements.