We had a business user leave the company who had a company supplied iPhone. Unfortunately the password was not provided to us, and the user deleted their iCloud account so we can reset their password to their work email and set a new password.
Proof of purchase from Verizon
Phone Number associated with phone
iPhone serial number
Press 2, then 3 for iOS
When connected to the support rep, explain that you have an iCloud-locked phone and that you would like to submit a request to have it unlocked.
Tell them that you have the IMEI for the iPhone in question and provide it when asked.
Apple may ask you for the invoice number, serial number and/or phone number of the iPhone to help them look it up on their end and verify ownership.
Once the Apple rep has provisionally established that your company, school or institution has ownership of the iPhone, they will send you an email with instructions on how to contact the group that handles unlocks of iCloud-locked phones.
Follow the instructions in the email and make sure to provide an electronic copy of the proof of purchase.