1. e4 e5 2. Nf3 d6 3. d4 Bg4 Wrong way, Black should play 3...Nd7 or 3...Nf6
4. dxe5 Bxf3 Now White can create pushing to f7 square
5. Qxf3 dxe5 6. Bc4 Nf6 Correct defence
7. 0-0 a6??? Wrong! Pawn at a6 dont create any troubles for white bishop. Black should play
7...Be7 or 7...Nbd7. Now White can attack...
8. Rd1 Qe7 Blocking bishop at f8. 8...Bd6 looks better
9. Nc3 Qb4??? How this move will help Black to defence? It looks like they dont understand that their king is in big trouble  
9...Nbd7 is a small chanse
10. Nd5 Qxc4 Strange move 10...Qd6 gives more chanses
11. Nxf6+ gxf6 Another way doesnt help - 11...Ke7 12. Nd5+ Ke6 13. Qg4+ Kd6 14. Nb6++ Nc6 15. Nxc4 winning the queen
12. Qxf6 The end. White wins anyway
Rg8 13. Qd8X.

Do you think 3...exd4 is playable?  

No, I think 3...exd4 should not be played, because Black simply "present" White central squares.

thanks. Happy Thanksgiving

As to 3........exd4 being playable, it is the most popular and probably the best!  Used by Svidler, Morosevich, and Bacrot in recent games from this decade, and for a century before that.

3....Nf6 is also playable, 3....Nbd7 and the game move are "playable" but can't be recommended.  The present of the central squares is given by playing 2......d6, not by move three.

Hard to find fault with Black's play through move six, as other choices aren't much better.

White's 7th misses the more forcing Qb3, forking b7 and f7, but O-O is good enough to keep a big edge, and give Black a load of problems.

7......a6?  triple ? is a bit strong!  Black must develop!  7.....Nc6 is relative best, and keeps him in the game.

White responds strongly with 8.Rd1?!, but misses the crushing 8. Qb3!

Black is obcessed with movement of his queen, when he ought to continue his development, with 8....Bd6.  After 8.....Qe7? White can only blunder away the win.

9. Nc3 is still not as strong as Qb3, but strong enough.

9.......Qb4??  9......c6 denies White the use of d5, and gives Black a glimmer of hope.  10. Bb3 works as well as the text, which is very tactical and forcing.  Black apparently blissfully unaware of his crisis.

12......Rg8????  Nd7 allows Black to continue a lost game, and exchange and pawns down, with his King still in deep poop.

Philadors can only be recommended by players who are willing to defend doggedly, while waiting for a slip by White.  Only a few modern masters will still employ it.

Regards,
WP

I can't agree more to woodpusher in that 7.Qb3 is the more (perhaps the most) forcing move. In my games so far, never be there any playable measure by Black to frustrate it.