Using the EN6362QI, the app note says vias on the ground under the part should be .33mm (.0129 inch). I have a board with microvias, .006 drill going to layer 2 ground and stopping. Will I have thermal issues? Do I need to go two more layers to hit the next ground? These hole are plated shut.
There is no issue with your vias design and the thermal performance will depends on how many vias you have between the PGND pad and the inner layer GND and increasing that vias will help to relief the heat from the part.
Also depends on what is Vout and the expected loading where increasing the Vout and the loading will generate more heat inside the package more than if the load or the vout is lower.
But if you you have the capability to connect the PGND vias to the other GND layers that will help to get better thermal performance.