Geometric structures are commonly encountered in natural and designed systems. However, the bottom-up fabrication of regular geometric assemblies with precise dimensional control, especially from soft materials, poses an outstanding challenge in contemporary materials science and chemistry. Herein, we present a general method for the preparation of colloidally stable, hexagonal platelets via the formation of crystalline inclusion complexes of tris-o-phenylenedioxycyclotriphosphazene and block copolymers bearing interactive blocks. Dictated by the screw dislocation growth of inclusion complexes, uniform hexagonal platelets with precisely controllable dimensions can be prepared. This supramolecular assembly approach is further utilized to produce concentric hexagonal platelets via stepwise seeded growth from various inclusion complexes.