"Our organization has all the phones on a single apple account and everyone is seeing each others call and text history and even voicemails"
I really recommend you don't do this, you'll likely have the account deactivated as it goes against Apple's T&Cs. Instead, use Managed Apple IDs via Apple Business Manager.
"You can have 10 devices (no more than 5 computers) associated with your Apple ID for purchases at one time."
https://support.apple.com/en-gb/118412