How was Gallifrey destroyed in Doctor Who?

Answer 1

Well there was a war between the Daleks and the Timelords and the Eye Of Harmony, which is an extremely powerful object that supported the planet Gallifrey, was opened because the Daleks wanted to use it to destroy the Timelords. Well, the timelords failed to stop the daleks from opening it, but Gallifrey was sacrificed to destroy the Daleks. The Doctor was the only Survivor, but what he didn't know was that some of the Daleks survived the blast and got out safely. They returned later in Season 1 of Doctor Who with Christopher Ecclecson and Billie Piper.

A possible weapon used to destroy Gallifrey was something called "The Moment", which was mentioned as being in the Doctor's posession on the last day of the war several times in the episode The End of Time (Part II), by the Time Lords themselves.

Answer 2

In "The Day of the Doctor" episode, it is revealed that Gallifrey was not actually destroyed, but instead frozen in a parallel pocket universe to protect it from the Time War.