You have a user in the portal showing an incorrect country prefix against their number. This may also be affecting their outbound calling.
How To Resolve.
Firstly, you will need to navigate to your Office365 Admin Centre and list the user. On the licensing screen you will be able to amend the country registered against the user.
Once amended click the 'Sync Now' button to read these settings from Microsoft 365 into the portal.
It can take an hour or so for this change to fully register so it is advisable to wait at least this long before returning to the portal where you should then perform a new Sync.