This study presents a multiphase engineering approach to develop stretchable phosphorescent polymers by combining stiffness and softness in well-designed block copolymers. The materials exhibit intrinsic stretchability of 712% and an ultralong phosphorescence lifetime of up to 981.11 ms. The block copolymers are synthesized via a two-step atom-transfer radical polymerization (ATRP) and subsequent hydrolysis process, resulting in amphiphilic polyacrylic acid-co-poly (alkyl methacrylate) block copolymers. The microphase separation in the copolymers enables the formation of distinct microdomains that contribute to the material's stretchability and phosphorescence properties. The hard PAA phase protects the phosphors, while the soft PBMA phase enhances stretchability. The copolymers demonstrate color-tunable phosphorescence in the visible range and can be used for multi-level volumetric data encryption and stretchable afterglow display. The study also shows that the multiphase engineering approach is applicable to a series of binary and ternary initiator systems, enabling the development of stretchable phosphorescent materials with enhanced mechanical properties, thermal and optical stability, and water resistance. The results demonstrate that the combination of a rigid microenvironment and soft phase provides a platform for achieving stretchable phosphorescent materials with long-lived phosphorescence. The study highlights the potential of these materials in various applications, including flexible electronics, soft robotics, intelligent sensing, and wireless communication. The research provides a fundamental understanding of the nanostructures and material properties for designing stretchable materials and extends the potential of phosphorescence polymers.This study presents a multiphase engineering approach to develop stretchable phosphorescent polymers by combining stiffness and softness in well-designed block copolymers. The materials exhibit intrinsic stretchability of 712% and an ultralong phosphorescence lifetime of up to 981.11 ms. The block copolymers are synthesized via a two-step atom-transfer radical polymerization (ATRP) and subsequent hydrolysis process, resulting in amphiphilic polyacrylic acid-co-poly (alkyl methacrylate) block copolymers. The microphase separation in the copolymers enables the formation of distinct microdomains that contribute to the material's stretchability and phosphorescence properties. The hard PAA phase protects the phosphors, while the soft PBMA phase enhances stretchability. The copolymers demonstrate color-tunable phosphorescence in the visible range and can be used for multi-level volumetric data encryption and stretchable afterglow display. The study also shows that the multiphase engineering approach is applicable to a series of binary and ternary initiator systems, enabling the development of stretchable phosphorescent materials with enhanced mechanical properties, thermal and optical stability, and water resistance. The results demonstrate that the combination of a rigid microenvironment and soft phase provides a platform for achieving stretchable phosphorescent materials with long-lived phosphorescence. The study highlights the potential of these materials in various applications, including flexible electronics, soft robotics, intelligent sensing, and wireless communication. The research provides a fundamental understanding of the nanostructures and material properties for designing stretchable materials and extends the potential of phosphorescence polymers.