Belladonna told us that her new place of employment has a policy.
The employees must hand in their phones at the beginning of the shift. The phones are returned at the end of the shift.
It is condition of employment.
The owners pay so much an hour for the employee's time and the owners expect full engagement in the job during each hour. More accurately, they don't want their customers to be inconvenienced by a distracted employee or to have the customer slowed down by an employee who slipped out of sight ("for just a minute") to play with his/her phone.