Not if they have no ability to reply to the user in the first place. The user may also be contacting support because they lost access to their account and not be able to access the identifying number.

If the user emails them they can certainly reply. It's just a matter of showing their email somewhere. The ID can be shown before the user logs in. That would not be less secure then relying on the email to reset the password. If someone is able to access the user's unlocked phone, they probably can access their email account too.