Phenax and SS

[redwolv]

So I had a guy who claims this.

{phenax, the god} is on the field and he plays {archer's Parapet}. He says he can tap the parapet right then and mill for 5. I said no, summon sickness prevents it from tapping for the ability. He claims cause the ability is from phenax and phenax doesn't have SS, he can.

Can i get a ruling?

[redwolv]

You have it. The creature gains an ability that includes {T} in its activation cost. Summoning sickness says that kind of ability can't be used unless you controlled that creature since your upkeep. Ergo, he has to wait.

You can FORCE a tap, but for different reasons.

For reference:

{Phenax, God of Deception}
and
{Chord of Calling}

Chord cares not for your sick summonings. Phenax does

Think you could find me the rule for this?

[Remillo]

302.6.: A creature's activated ability with the tap symbol or the untap symbol in its activation cost can't be activated unless the creature has been under its controller's control continuously since his or her most recent turn began. A creature can't attack unless it has been under its controller's control continuously since his or her most recent turn began. This rule is informally called the "summoning sickness" rule.

The important thing here is Phenax is granting the ability to the creature.  You're not tapping the creature to activate Phenax's ability, but rather to activate an ability of that creature.