At some point in the past, they had a peaceful and advanced society and proclaimed themselves the task of spreading peace and order throughout the galaxy. Unfortunately, the arrival of an Earth fugitive scientist from the eugenic wars in the 22nd century inadvertently brought an infectious Earth bacterium to Phylos which nearly wiped out the entire species. The outcast scientist Dr. Keniclius helped to save the surviving Phylosians and later became their leader, convincing them that they shared the same goal of creating galactic peace. The Phylosians in turn helped Keniclius with his projects of genetic augmentation and cloning, which they believed would be the dawn of a better galaxy.
After nearly a century of isolation the planet was visited by the Enterprise crew, which convinced the Keniclius clone and the Phylosians that the interstellar chaos of the previous century had already been converted in a more peaceful and prosperous state through the establishment of the United Federation of Planets. After the Enterprise visit, the Phylosians turned to direct their efforts into recreating their own civilization, with the help of the augmented clones of Keniclius and Spock (the later of whom had been kidnapped and cloned by Keniclius 5 while on the planet).