Forum:Gladiator Beast Returning to Deck

These cards state that If this card attacked or was attacked, you can return it from the field to the deck at the end of the Battle Phase. My friend tells me that I can't activate a Gladiator Beast effect if my opponent goes directly from his Battle Phase to his End Phase. If that is true, then when am I suppose to activate their effect. Please explain in detail when I can activate their effect.