At the time of writing, this does not yet seem possible with Graph API, and requires the Teams Powershell module instead.

Open PowerShell, and install the PowerShell Teams module:

Install-Module -Name MicrosoftTeams -Force -AllowClobber

Connect to the Microsoft Teams service:

Connect-MicrosoftTeams

List all users and their assigned numbers. Export to CSV if needed:

Get-CsOnlineUser | select DisplayName, UserPrincipalName, LineUri | Export-Csv -Path TeamsNumbers.csv

• https://learn.microsoft.com/nl-nl/microsoftteams/teams-powershell-install