We construct a taxonomic framework for the observational detection of physical coherence across astrophysical and cosmological domains. Five operationally distinct classes are defined — phase coherence (I), temporal coherence (II), morphological coherence (III), kinematic coherence (IV), and structural multi-scale coherence (V) — each mapped to specific instruments, public data archives, and quantitative proxy observables. We show that several well-known cosmological phenomena can be consistently classified within this framework as observational manifestations of primordial phase coherence. This paper does not claim direct detection of the RCD coherence field C; rather, it defines operational proxies through which different forms of coherence may be placed in contact with observations. The framework provides the operational vocabulary for the RCD observational series (Papers XX-XXVI) and establishes falsifiability criteria for the program.