If you're using Directory Synchronization together with an on-premises AD DS, populate the telephoneNumber attribute that uses the E.164 formatted telephone number, and let the attribute sync to Microsoft Office 365.
Note It can take up to 24 hours for changes that you make in the portal or on-premises to be visible in a user’s Lync contact card.
If a telephone number isn't entered by using E.164 format in the Office 365 portal or in the on-premises AD DS, it won't replicate to the Lync address book or it may appear in an unexpected format.
Note Unexpected formatting can also occur when a user has an Outlook contact who has the same number as the Lync contact. This data can sometimes be merged and results in an unexpected format. Disabling Personal Information Manager (PIM) integration can help locate the source of such an occurrence. The recommended action is to remove or change the Outlook contact to match the Lync contact information.
Article ID: 2658120 - Last Review: Dec 28, 2016 - Revision: 1