Can an employee created through Microsoft Azure AD have an external phone number?

Yes. The external phone number will appear under the contact in Myfone.

You can note the customer's numbers during the Felter (Fields) step in Microsoft Azure AD. The numbers will be displayed under the contact in Myfone, regardless of whether the number is with Flexfone or not.

If the employee's number from Microsoft Azure AD is not with Flexfone, Flexfone does not assign a phone number to the user but simply creates an employee in the PBX.