Activate Phyrexian Altar by sacrificing Child of Alara, adding one mana of any color.
Child of Alara dies, triggering itself and Gift of Immortality.
Resolve the Child of Alara trigger, destroying all nonland permanents you don't control due to your permanents having indestructible.
Resolve the Gift of Immortality trigger, returning Child of Alara from your graveyard to the battlefield.
At the beginning of the next end step, Gift of Immortality triggers, returning itself from your graveyard to the battlefield attached to Child of Alara.
Repeat each turn.
Results
Destroy all nonland permanents you don't control each turn.