The authors thoroughly investigate the development of the diachronic phonology conceptual framework. The formation of phoneme concept as well as the evolution of the term “phoneme” itself falls within the scope of our research. A great attention is paid to the linguistic-historiographic analysis of the works of the Moscow, Prague and Saint Petersburg phonological schools’ representatives, which were dedicated to the problem of the language phonemic system. The fundamental statements of the XX century’s scientists on the necessary consideration of the phoneme functional load in the language system are defined. In view of the functional load of each phoneme in the system we study the uprising of the hyperphoneme notion, namely the development of its term base in the works of M. V. Panov, distinguishing the hyperphoneme from the archiphoneme of Prague linguists. The contributions made by the linguists of the XX century in the practical study of phonological systems of the subgroup of Eastern-Slavic languages are reconsidered in the article.