But that was Rachel,and at the time of the what if she was still limited in the use of her powers.
It wasnt up until the battle with Necrom that she let loose with the Phoenix.In Excalibur she was even beaten by the robot version of Twitty from the Looney Tunes.
Nevertheless the handling of the phoenix in the what if was very bad.Rachel+Phoenix should have been alone in the Multiverse.Other versions of Rachel across the Multiverse didnt bond with the phoenix,this was even confirmed by Roma.
Phoenix vs. Tribunal
The Living Tribunal would win hands down. Mainly because he is basically the judge of all things that happen in the Marvel Universe. Meaning that even if he's not stronger (which I strongly disagree with), he still has jurisdiction over the Force due to him carrying out the will of TOAA. Raw power doesn't even come into question. He tells everyone what to do, and if you don't like it then you have to answer to his boss. And as far as Phoenix being able to hold the universe in her hands, the Tribunal has the power to destroy the Multiverse if necessary, as stated before. Shaq can hold a marble in his hands, but does that mean he can crush it?