IPhone Set up for small to medium size business to be used by employees
You should consider using an MDM solution for managing the enterprise devices.

If you simply hand out devices to users to set them up themselves, and they log in with their Apple ID, the devices remains associated with their Apple ID unless the user explicitly removes it or log out of it.

This may be cumbersome and difficult to manage. Using an MDM solution to centrally manage and pre-configure the devices for employees would be the recommended approach. The MDM solution also makes it possible and easy to manage usage policies. It would also make it easy to pass around the device to a different employee.