Enable the routing of Teams meeting dial-out calls through Direct Routing Teams meeting dial-out calls are initiated from within a meeting in your organization to PSTN numbers, including call-me-at calls and calls to bring new participants to a meeting.
To enable Teams meeting dial-out routing through Direct Routing to on-network users, you need to create and assign an Audio Conferencing routing policy called "OnlineAudioConferencingRoutingPolicy".
Note:
Direct Routing lets you connect a supported, customer-provided Session Border Controller (SBC) to Phone System. With this capability, you can configure on-premises Public Switched Telephone Network (PSTN) connectivity with Microsoft Teams client, as shown in the following diagram:

Reference:
https://learn.microsoft.com/en-us/microsoftteams/audio-conferencing-on-network
https://learn.microsoft.com/en-us/microsoftteams/direct-routing-plan