Upon their discovery on Phylos, Captain Kirk theorized these ships to be "a technology possibly greater than anything we 'animal' species [have created]." Doctor McCoy noted that the ships, which were covered in vines, never got off the ground, as a result of the great plague that affected their people, and wondered aloud what their intended purpose was before they became a more peaceful people.
It was later revealed by Agmar, that their fleet's intended purpose coincided with Keniclius's, to "carry out [their] own plan to impose peace on a galaxy that knew none." Ultimately, the fleet remaimed grounded, as the Phylosians, with the assistance of Keniclius 5 and Spock 2, could focus on rebuilding their own society. (TAS: "The Infinite Vulcan")