Two iPhone 4S Configured with same email ID
In your former iPhone:


Tap Settings > iCloud. Scroll down and tap Sign Out. In iOS 7 or earlier, tap Delete Account.
Go to Settings > General > Reset > Erase All Contents and Settings. 



  In iOS 7 or later with Find My iPhone turned on, you'll need your
  Apple ID and password.


Additionally, 


  if you're using iCloud and Find My iPhone on the device, sign in to
  icloud.com/find, select the device, and click Erase. After the device
  has been erased, click Remove from Account.


Get your former employer to set up the old iPhone with other Apple ID.

Check this article on Apple Support for more information.