This study examines the doping mechanism in the intermediate concentration regime of solution-based chemical doping, a common approach to enhance the electrical properties of conjugated polymers (CPs). Although doping levels generally increase with dopant concentration, the relationship is non-linear. Through systematic electrical, optical, and morphological characterizations, a distinct phase transition was identified in the intermediate regime. In this region, doped films exhibit anisotropic deformation, characterized by out-of-plane expansion and in-plane contraction, which induces internal stress and leads to the formation of nano-scale cracks. While prior studies have primarily focused on low doping levels for transistor applications or high levels for thermoelectric devices, this work emphasizes the critical role of the intermediate regime. These findings provide important insights for developing advanced doping strategies to improve the performance.