The Greek force was there to bloc the Persian advance into southern Greece in order to precipitate a sea battle in the nearby strait of Artemesion in which the Greeks hoped to destroy the Persian navy and remove its threat to the Greek cities. The sea battle went on for three days, and the Greeks lost. The holding force at Thermopylae, no longer required, withdrew. The Spartan and Thespian contingents selflessly remained holding the pass to cover the withdrawal and were all killed.
The narrow coastal pass of Thermopylae . August or September 480 BC
The Phoenicians were not anywhere near the Thermopylae Pass, so they could not betray the Greek force there.
the pass is called "The Pass of Thermopylae"
The pass at Thermopylai is still there.
See:What_was_the_battle_at_Thermopylae_involving_the_300_and_who_won
Thermopylae
Sparta
The pass at Thermopylai remains to this day.
At its narrowest, about 100 metres.
There was a pass at Thermopylai (hot gates - a thermal springs area).
The pass of Thermopylae.
Thermopylae(?)