Call2Teams - Customers
The reason for this is that the user has been given the Virtual Phone System Licence rather than the regular Phone System Licence. All you need to do is amend the Phone System Licence and the error will clear on the next Sync.
The Virtual Phone System licence should be reserved for Service Accounts.
Microsoft are changing the name of the Phone System Licence to Teams Phone Licence. Please be aware that references to both may continue to co-exist for a time.