Indestructible (Effects that say "destroy" don't destroy that permanent. An indestructible creature can't be destroyed by damage.)
As long as your
devotion to blue
(Each
in the mana costs of permanents you control counts towards your devotion to blue.) and black is less than seven, Phenax isn't a creature.
Creatures you control have "

: Target player
mills (To mill a card, a player puts the top card of their library into their graveyard.) X cards, where X is this creature's toughness."