Now that's the hard part, collision means the objects are overlapping, meanwhile you could check relative positions, that presumes that you'll never have any tunneling problems. (This will work if your frame rate is high and your player moves slowly). However, another way to check is by checking the player's velocity at the time of the collision.
You could just try checking Player.Platform.MoveAngle > 180 (This should make it so that you can only break bricks while moving upwards).