Black might also consider 2....c5 with a Sicilian formation.
This and not 3.Nf3 Nc6 etc. when White really cannot hope for an advantage. The thrust with f4 is more in keeping with the fighting spirit of the Philidor's Defense, which White is playing in reverse. Black must react energetically, and the opening play here is interesting for theory.
On 4.fxe5 Nxe5 5.d4 Ng6 6.e5 Ne4 followed by d5 etc. and White gains nothing. Em. Lasker recommended the interesting idea 4.fxe5 Nxe5 5.Nf3 Nxf3+ 6.gxf3! to gain more central pawn control. But Black can respond with 6....Nh5 7.Be3 Bd6!? fighting for control of the dark squares. With the text move White hopes to force d7-d6, blocking in Black's dark-squared Bishop. Black's next move shows his intentions not to play passively.
White probably has nothing better than to take the d-pawn, since 5.fxe5 dxe4! 6.exf6 exf3 7.Qxf3 Nd4! 8.Qe4+ Be6 9.fxg7 Bxg7 10.Na3 O-O appears to give Black a strong initiative for his sacrificed pawn.
Or 7.c3 Ne5! 8.Qe2 Bd6 9.d4 Bxf3 10.gxf3 Qh4+ 11.Kd1 O-O-O 12.dxe5 Rhe8! when Black's attack more than compensates for the sacrificed piece.
The threat of mate at f7 allows the Knight at d5 time to continue his adventures. The Knight will eliminate one of White's two Bishop's, and the resulting Bishops of opposite color will aid Black's attack on the White King.
Or 14.Nf2 Ne5 15.Ng4 Nxg4 16.Bxg4+ Kb8 and Black is better.
White will not be able to hold onto his extra pawn. For example, if 15.Qd1 Rhe8 16.c3 Nxf3 17.Qxf3 Rxd3 18.Qf5+ Rd7 19.Rad1 Qa6+ 20.Ne2 Qe6 21.Qxe6 Rxe6 with a winning ending for Black.
Black also wins after 18.c3 Nxf3 19.gxf3 Rxe5.
Winning at least a piece since 20.Qb4 a5! followed by Nxf3.
Notes based on those of Alexander Alekhine