Please follow these steps to check whether the caller ID policy for this user is correct: Sign into Microsoft Teams admin center>Voice>Caller ID policies.
Based on my knowledge, admin could control the use caller ID policies to change or block the caller ID (also known as calling line ID). You can use caller ID policies to display an alternate phone number for Teams users in your organization, block the outbound phone number, block an incoming number from being displayed, or set the Calling Party Name (CNAM). For example, when a user makes a call, you can change the caller ID to display your organization's main phone number and company name instead of the user's phone number.
For more details about its settings, you could refer to:
https://learn.microsoft.com/en-us/microsoftteams/caller-id-policies#create-a-custom-caller-id-policy
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