Answer:
To lessen the distractions and possible blackmail.
Step-by-step explanation:
Without the phone the worker can't constantly check their phones for social media and texting is controlled. The blackmail possibility is lessened because someone's phone isn't just sitting on their desk where other people can hack or just open it and possibly see something you didn't want them to see.
Hope this helps, have a good day/night. Stay safe :)