The Phylosians developed into a technologically advanced civilization. They had a naturally long lifespan, which was further extended by their greatly advanced medical science. At some point in their history, the Phylosians set about the task of enforcing peace in the galaxy. They built a fleet of large Phylosian starships, intending to use them for this task, but other events intervened.
Stavos Keniclius, a Human scientist, visited Phylos in search of what he called a perfect specimen. However, Keniclius was a carrier of a non-native, staphylococcus strain of bacteria that nearly destroyed all life on Phylos. He worked to save the Phylosians from his disease. Thanks to his work during the Eugenics Wars, he was able to create many clones of himself, in an attempt to undo the damage he caused. The Phylosians eventually referred to Keniclius as "the Master." When it became known that Keniclius had the same goal of imposing peace throughout the galaxy with a master race of clones, the Phylosians agreed to help Keniclius in acquiring the perfect specimen to copy.
When the USS Enterprise visited Phylos in 2269, Stavos Keniclius 5, the fifth clone of the original Stavos Keniclius, chose Spock as the perfect specimen. He cloned Spock, creating Spock Two. However, the galactic chaos that Keniclius had hoped to combat no longer existed, thanks to the work of the Federation. Keniclius decided to give up the plan to create the army of clones, and instead planned to work on the problem of saving the Phylosian species. Spock Two also remained behind to help Keniclius with this task. (TAS: "The Infinite Vulcan")