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

Return flights

25 Aug - 03 Sep	Aer Lingus
17 Aug - 26 Aug	British Airways	direct
13 Aug - 27 Aug	TAP
16 Aug - 25 Aug	Spirit Airlines
19 Aug - 24 Aug	Spirit Airlines
24 Aug - 30 Aug	Frontier Airlines
13 Aug - 21 Aug	Spirit Airlines
25 Aug - 03 Sep	Finnair	direct
27 Aug - 06 Sep	TAP
16 Aug - 25 Aug	British Airways	direct
28 Aug - 07 Sep	TAP
14 Aug - 01 Sep	Frontier Airlines
22 Aug - 31 Aug	Aer Lingus
11 Aug - 19 Aug	Frontier Airlines
11 Aug - 18 Aug	Spirit Airlines
27 Aug - 03 Sep	United
31 Aug - 07 Sep	United
25 Aug - 01 Sep	United
29 Aug - 05 Sep	United
28 Aug - 07 Sep	British Airways	direct

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

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 August from 583€

Return flights