I'm not sure of the best place for this conversation, so starting here.
We have a user who has somehow managed to get his personal mobile number into hisOutlook/OWAprofile. He has not done this intentionally. It is not recorded in our on premise AD, but appears if you look at his contact details via Outlook, or via OWA. (In Outlook the number appears twice, formed slightly differently).It does not appear via Delve. It is present in this EoL contact properties.
If I try and edit his properties in EoL contact properties, it won't save it because the account is synced to on premise AD.
Any ideas how this may have occured or how we can rectify it. Being a service desk engineer he really does not want his personal number advertised to the whole org!
They certainly have not done this intentionally. If an admin cannot modify someone's contact info settings when the O365 AD is synced to the on premise one, I'd be very surprised if a user can, even if they had permission to edit their contact info.