Phase Detection AF is not working with the mount adapter and an attached A-mount lens.
If you are using the LA-EA1/LA-EA3
ILCE-7RM2: When a SSM/SAM lens is mounted, you can select Phase Detection AF or Contrast AF for AF System in the Custom menu.
Other than ILCE-7RM2: When a SSM/SAM lens is mounted, you can adjust the focus using Contrast AF.
If you are using the LA-EA2/LA-EA4
You can adjust the focus using the Phase Detection AF that is built in to the LA-EA2/LA-EA4.