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

Return flights

29 Sep - 10 Oct	Aer Lingus
09 Sep - 15 Sep	Air Canada
27 Sep - 21 Oct	TAP
26 Sep - 23 Oct	Frontier Airlines
20 Sep - 01 Oct	Aer Lingus
21 Sep - 01 Oct	Frontier Airlines
24 Sep - 30 Sep	jetBlue
22 Sep - 01 Oct	American Airlines
20 Sep - 31 Oct	Spirit Airlines
14 Sep - 18 Sep	Spirit Airlines
20 Sep - 29 Oct	Spirit Airlines
30 Sep - 25 Oct	Aer Lingus
20 Sep - 28 Oct	British Airways
10 Sep - 20 Sep	Spirit Airlines
16 Sep - 19 Sep	Frontier Airlines
07 Sep - 11 Sep	Spirit Airlines
11 Sep - 23 Sep	Spirit Airlines
25 Sep - 28 Sep	Spirit Airlines
07 Sep - 27 Sep	Spirit Airlines
07 Sep - 14 Sep	Spirit Airlines

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 $643

Return flights