Activate Phyrexian Altar by sacrificing Nether Traitor, adding .
When Nether Traitor dies, Field of Souls triggers, creating a creature token.
Activate Phyrexian Altar by sacrificing the creature token, adding one mana of any color.
When the creature token dies, Nether Traitor triggers, causing you to pay to return Nether Traitor from your graveyard to the battlefield.
Repeat.
This loop sets up an endless cycle of sacrifice and resurrection by letting Phyrexian Altar convert your creatures into the black mana needed to fuel Nether Traitor's triggered ability from the graveyard. Meanwhile, Field of Souls acts as a vital translation piece, turning the loss of your nontoken creatures into the sacrificial Spirit tokens required to keep the altar churning. Because Nether Traitor returns directly to the battlefield each time a creature dies, you can continuously repeat this process to generate infinite colored mana along with an endless stream of sacrifice, death, ETB, and LTB triggers.