The design of block-copolymer-based functional materials, including mesoporous membranes and nanoparticles, requires a comprehensive understanding of the hierarchical assembly of block copolymers in selective solvents into micelles and subsequent ordered phases. It is hypothesized that micellar ordering and characteristic assembly can be described using a set of phase parameters that account for entropic and enthalpic interactions. Dissipative particle dynamics (DPD) simulations are used to systematically investigate the self-assembly of semidiluted block copolymers, resembling isoporous membrane preparation conditions. The effect of Flory–Huggins interaction parameters, block lengths, and concentration on the morphology and polydispersity of the micelles is evaluated. The interaction parameters are mapped into Flory–Huggins theory by considering the block's conformation. These results reveal the effect of polymer concentration and solvent affinity on the morphological transition of the aggregates, in agreement with existing experimental evidence. It is identified that monodisperse-spherical micelles in solution are fundamental to stabilize ordered states. Weak solvent segregation of the largest block, curvature of the core-corona interface, and stretching of the corona-forming one are found to be key to stabilize monodisperse assemblies. These conditions can be predicted using spherical-micelles packing considerations and a global phase parameter from the Flory–Huggins theory. This study provides valuable insights into the self-assembly of diblock copolymers and offers a potential way to optimize the preparation of mesoporous ordered structures and micelle ordering in semidiluted systems.