AirHint found the following cheapest return flights from Philadelphia (PHL) to Lisbon (LIS) in September 2025 (see full year).

Return flights

24 Sep - 30 Sep	American Airlines
23 Sep - 05 Oct	Frontier Airlines
25 Sep - 28 Sep	British Airways	direct
18 Sep - 25 Sep	Frontier Airlines
30 Sep - 25 Oct	TAP
20 Sep - 27 Sep	Frontier Airlines
18 Sep - 25 Sep	British Airways	direct
20 Sep - 27 Sep	Iberia	direct

Also check the deals for one-way flights from Philadelphia to Lisbon in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from Philadelphia to Lisbon in September from 651€

Return flights