What is the Most Important Phase of a Chess Game

I personally think it's the endgame because all your opening/middlegame strategies usually lead to a winning endgame

middle game > endgame > opening
Proof: play against a strong engine, it will destroy you with middlegame tactics regardless of opening imposed on it. You will not make it to the endgame. That is why below grandmaster level chess is decided in the middle game.
"Chess is 99% tactics" - Teichmann
"Before the endgame the Gods have placed the middle game" - Tarrasch
Only when both players are strong at offensive and defensive middle game tactics the game goes to an endgame. Carlsen wins most of his games in the endgame.
Only when both players are strong at tactics and endgames does the opening play a role, like in ICCF or in World Championship matches.

I agree with post #2 

Middle game is the most important stage, even if you don't come out of opening, you still can outplay your opponent in the middle game.