He never did. As revealed in "The Day of the Doctor", The first 13 incarnations of the Doctor moved Gallifrey into a pocket universe of its own. When he did this, the Dalek fleet was surrounding the planet & firing on it from all directions. As soon as the planet vanished, the Daleks' intense firepower had nothing to hit but their own ships. That destroyed them in a huge explosion, which made it seem as if the planet & the Time Lords had also been destroyed.