Yet creating or destroying a universe is nothing to a phoenix avatar. Jean as phoenix of the white crown telekinetically reformed a universe and rewound its timeline to get rid of a possible future. This was done on a whim. This happened in New Xmen at the end of the 'Here Comes Tomorrow ' story arc
The M'kraan crystal when unleashed was momentarily blinking out the multiverse and all its alternate realities. Despite Jean contained this effect and reenergised the energy matrix which held the neutron galaxy in place. She basically held together existence as it was coming apart at the seams. That is one of the highest feats ever achieved by any being in Marvel Comics.
Phoenix was also the being responsible for linking all the alternate realities and universes in the multiverse together. It projected a doorway through each every different reality.
Krona pales in comparison to what jean as the phoenix of the white crown can do. Sorry guys.