Universal Rule.
The first time a Phoenix loses its last Health Point, the owner must roll a D6. On a roll of 5+ (or 3+ if the model has Warden's Bond), remove the model and place a marker where its centre was. If the roll fails, the model counts as a casualty. Otherwise, at the start of step 3 of the Movement Phase Sequence (after Rallying Fleeing units) in the next Player Turn, the Phoenix model is placed back on the Battlefield. The centre of the model must be placed within 3" of the marker and the model must be placed more than 1" away from other units and Impassable Terrain, facing any direction (if this is not possible, the Phoenix cannot return and counts as a casualty). The returned model is the same model that left the game, including any and all ongoing effects (such as spells affecting the model), with the exception that it always returns with only 1 Health Point left and counts as Rallied in case it was Fleeing when it lost its last Health Point (and thus is Shaken until the end of the Player Turn).