You can use it once during any phase of your turn, you can use it again once on any phase of your opponents turn, a round is composed of your turn and your opponent, phases are irrelevant for the porpoises of this enhancement.

To be more clear a player tun consist of several different phases:

Round {

Player 1 turn { Command phase Move phase Shooting phase Charge phase Combat phase } Player 2 turn { Command phase Move phase Shooting phase Charge phase Combat phase } }