Frontier encourages passengers to check in online or through their mobile app before arriving at the airport. However, if you need to check in at the terminal, the check-in counters and self-service kiosks are located near the entrance of Terminal E. Arrive early—especially during peak travel times—to clear security, which is usually efficient but can experience delays during busy hours. https://airportsterminalhub.com/airlines/frontier-airlines/frontier-airlines-philadelphia-international-airport-phl-terminal/