Phone System in Microsoft 365 provides a default caller ID that is the user’s assigned telephone number. You can either change or block the caller ID (also called a Calling Line ID) for a user.
You can learn more about how to use caller ID in your organization by going How can caller ID be used in your organization.
By default, the following caller ID settings are turned off. This means that the Teams user’s phone number can be seen when that user makes a call to a PSTN phone. You can change these settings as follows: