Be alert to time wasting; the employee who is on the phone, whether land line or cell, taking and making personal calls, is to be spoken to once. Then, if it continues, discharged.
If one can not draw a line between work and private life, then they can’t be working for you. They are just there to get the salary and are living their lives, doing what they want at your expense.
People who can not differentiate between doing the work they are paid for and having a private life, can not be considered good employees. Your work comes after their various chores and interests.
Further, those who babble on the phone are scattered. They will make stupid mistakes, they will not pay attention, and your work will suffer.
Every employee should arrive ready to work. They should think about what they are doing. They should not be distracted.
The cell phone is the greatest weapon you have; it is the most revealing. Sure, if there is an emergency, and the call is emergency, you’ll know by the tone of voice, the posture, the need to leave; but 99.99999% is just babble.
And you don’t need to pay anyone to babble.