Consider the following scenario in Microsoft Skype for Business 2016:
You have a user who is not enabled for Skype for Business 2016.
The user has two or more phone numbers in Active Directory.
You choose to dial one of the phone numbers from the user's contact card.
In some cases, the number that is dialed is not the number that you chose.
The Skype for Business 2016 client prioritizes one property above others. This causes the client to consistently call the same number of a given user, regardless of the number that is chosen.
To fix this issue, install the October 6, 2020, update (KB4486669) for Microsoft Skype for Business 2016.