First is to just wait on the side of a road for an unoccupied one to pass and raise your hand. This will signal them to stop in order to pick you up. Taxi are everywhere in Greece so this way works most of the time. The second way is to go to a square or central area where a lot of taxis always gather.
What taxi app do they use in Greece?
With iMove Greece booking app you can call a cab ride across Greek islands (Mykonos, Paros, Naxos, Santorini) & Athens car transport.