2D perovskite structures have gained significant attention due to their reliable long-term stability. Unlike quasi-2D perovskites, phase-pure 2D perovskites exhibit a flattened energy landscape and low energy transfer losses, offering substantial benefits for enhancing device efficiency and stability. Recent research on phase-pure 2D perovskites has shown significant progress, attributed to their unique properties. This review delineates advancements in the study of phase-pure 2D perovskite materials and elucidates the relationships between crystal structure design, growth, and device performance regulation. Additionally, it summarizes techniques for characterizing phase-pure 2D structures and methods for their precise synthesis. Finally, an outlook on the future development of phase-pure 2D perovskites, highlighting the scientific and technological challenges in current research is provided.