You will need to Add a Custom Attribute to the Okta User Profile and map it to Office 365 Field and also Map the AD field to the New Customer Attribute.
To Create the Custom Attribute: 1. Directory 2. Profile Editor 3. Select the Okta - User profile 4. Click on Add Attribute 5. Fill out the form and save it.
To Map from AD to Okta 1. Select the Profile Mappings tab 2. select edit Mappings for Active Directory 3. on the 1st tab (AD to Okta), scroll down to find your new custom attribute 4. select the AD field that corresponds (appuser.facsimileTelephoneNumber) 5. Preview it one of your users 6. Save Mappings
To Map from Okta to O365 1.Select the Profile Mappings tab 2. select edit Mappings for O365 3. on the 2nd tab (Okta to O365), scroll down the O365 User Profile to find FacsimileTelephoneNumber, and map it to the New Custom field. 5. Preview it one of your users 6. Save Mappings