When Phyrexian Devourer's power is 7 or greater, sacrifice it.
Exile the top card of your library: Put X +1/+1 counters on Phyrexian Devourer, where X is the exiled card's converted mana cost.
9/22/2011 Phyrexian Devourer’s first ability continually checks its power as a state trigger. Once it triggers, it won’t trigger again as long as the ability is on the stack. If the ability is countered and the trigger condition is still true, it will immediately trigger again. If the ability resolves, you’ll have to sacrifice Phyrexian Devourer even if its power has been reduced to 6 or less by then.