The reflex phase is one of two phases during a game turn. A reflex phase for a player occurs simultaneously with their opponent's active phase.

During the reflex phase a player carries out reflex actions as indicated on their model cards, when the criteria for the reflex trigger is fulfilled. If a player does not carry out a reflex action the first time it is valid, the player loses the opportunity to use it in that phase. Reflex actions are mandatory, and can be enforced by the active player. Where multiple models have reflex triggers they are carried out out one at a time, until either the reflex trigger is no longer valid or all reflex actions have been carried out. The player who is in their reflex phase chooses the order in which multiple reflex actions occurs. 

The reflex phase is sometimes referred to as the reflex turn, and the player in their reflex phase sometimes referred to as the the reflex player.