A planet located near the edge of the galaxy, recently discovered by the United Federation of Planets as of 2269. Phylos is a world dominated by plant species rather than by animal life forms, and is home to a race of sentient, ambulatory plant-beings who have constructed at least one large city on its surface, a city that seems to be largely in ruins by the middle of the twenty-third century.

Dr. Stavos Keniclius 5 used Phylos as his base of operations for his plans to create a army of genetically engineered supermen in order to "enforce? peace throughout the galaxy. After Captain Kirk and Commander Spock dissuade Keniclius 5 from this scheme on stardate 5554.8 (2269), Keniclius 5 remained on Phylos to help the Phylosians restore their civilization to its former glory, with the help of a giant clone of Spock.