He’s not a copy or a clone. As the Doctor says in the episode, teleporters ‘break down living matter and information, and transmit it. All you have to do is add energy’. ‘Transmit’ is the key word here. The energy to activate the teleporter comes from the Doctor burning his dying body, while the information and matter required to generate his ‘new’ body are always the original transmissions- what else could they be? The room resets to the state where the Doctor’s original body was an incoming transmission, and it’s in that state that he fires up the teleport. Confusingly, it’s always the original matter from his original body being used, over and over again. That’s an ‘energy loop’.