What terminal is Frontier Airlines at PHX? Terminal 3 at Phoenix Sky Harbor International Airport (PHX) serves as the departure point for most of Frontier Airlines’ domestic flights. This terminal offers a range of passenger services, including ticketing counters, baggage claim, and several dining and shopping options. However, for flights to destinations like Cabo San Lucas, Frontier use Terminal 4, which is designated for international travel. Travelers may easily navigate between airports using the complimentary PHX Sky Train. Checking your specific flight details in advance is usually advisable because terminal assignments may vary from time to time.