Migratory aptitude in Baeyer–Villiger reaction
In the following image you can see the charge distribution in the transition state of the Baeyer–Villiger reaction (image taken from Clayden Organic Chemistry):


As you can see, there is partial positive charge at the migrating C atom, therefore a group will migrate easier if it contains cation stabilizing moieties. A benzene ring significantly stabilizes positive charge in its proximity through delocalization.