Final answer:
The leading first-phase modernist composers include Igor Stravinsky, known for 'The Rite of Spring', Arnold Schoenberg and his development of the twelve-tone technique, and Béla Bartók who infused Hungarian folk elements into his work.
Step-by-step explanation:
Three of the leading first-phase modernist composers were Igor Stravinsky, Arnold Schoenberg, and Béla Bartók. These composers played significant roles in challenging and redefining the musical landscape of the early 20th century. Stravinsky, with his groundbreaking work 'The Rite of Spring', used dissonant harmonies and complex rhythms to evoke the primal energies of ancient rituals. Schoenberg ventured into atonality and later developed the twelve-tone technique, which abandoned the traditional tonal harmony altogether. Bartók, inspired by the folk music of his native Hungary, integrated these influences into his compositions, adding an element of nationalism to the modernist movement.