When this issue occurs, Microsoft Lync 2013 only shows a user's telephone number in E164 format in a toast notification. This issue occurs when reverse number lookup (RNL) is invoked and you are enabled for the Enterprise Voice feature.
Note Lync 2013 will show the user's display name when you receive next calls from the user.
Note Lync 2013 will show the user's display name when you receive next calls from the user.