Hi Detlef,
The Lock screen is displayed when the phone is locked (inactive). Your system administrator may disable the screen lock during your work hours. By default, the home screen is displayed when you unlock your phone. You can configure your phone to unlock to the phone application.
Phone Only Mode limits the user access on the phone to the home screen, Phone application, Contacts application, and Settings application. The user cannot add shortcuts or widgets to the home screen in Phone Only Mode.
Thanks and Regards,
Geevarghese