Nether Traitor dies, triggering Pawn of Ulamog, crating a 0/1 Eldrazi Spawn creature token.
Activate Phyrexian Altar by sacrificing the Eldrazi Spawn token, adding one mana of any color.
The Eldrazi Spawn dies, triggering Nether Traitor, causing you to pay ({B} magic symbol) to return Nether Traitor from your graveyard to the battlefield.