The Polish scholar Jan Baudouin de Courtenay (together with his former student Mikołaj Kruszewski) introduced the concept of the phoneme in 1876, and his work, though often unacknowledged, is considered to be the starting point of modern phonology. He also worked on the theory of phonetic alternations (what is now called allophony and morphophonology), and had a significant influence on the work of Ferdinand de Saussure.
When was the phoneme as a concept introduced?
1876