Charged polymers ubiquitously play a crucial role in numerous biological and synthetic systems, exhibiting diverse phases and self-assembly behaviors due to the entanglement of polymer connectivity and long-range electrostatic interactions. Charged polymer physics delves into understanding their highly coupled and non-linear response, shedding light on comprehending biological systems composed of charged biopolymers. Inspired by biomolecular condensates, membrane-less organelles assembled by intrinsically disordered proteins within cells, we aim to explore the phases and self-assembly in complex charged polymer solutions, where complexities stem from the chemical sequences and physical associations of polymers. These complexities cause difficulties in responding to the growth interest of biomolecular condensates. Employing the field theory formalism and statistical properties of conformations, we address the connectivity and interaction into the spatial correlation of monomer concentration, leading to the Landau free energy predicting the formations of phases and self-assembly. This thesis comprises two works. The first work focuses on predicting the stability, size, and morphology of microphase separation for sequence-specified charged polymers, resulting in machinery for microphases for general sequences. In the second work, utilizing polyzwitterions as a simplified model for associative charged polymers, we explore the thermoreversible behaviors of electric-dipole-driven macrophase separation and gelation. Furthermore, our use of the renormalization group reveals that concentration fluctuations near critical points deviate from the Ising universality class due to the presence of associations. These results can facilitate future investigations on more complex systems in biological and synthetic realms with suitable modifications.