Start an Audio Conference Over the Phone Without a PIN in Microsoft Teams

You can set it up so that anyone can dial in to a meeting and not be prompted for a PIN to start the meeting. You can use the admin center to enable or disable this setting for a single user.

A PIN isn't required for the meeting organizer if someone has started the meeting from the Microsoft Teams app. A PIN is only required when a meeting organizer joins their meeting over a phone. The PIN for meetings is sent to the audio user when they are assigned the Audio Conferencing license and are enabled for Audio Conferencing.

Enable or disable anonymous callers from joining a meeting

1. Log into the Teams Admin Center.

2. In the left navigation, click Users.

3. Select a user in the list, and then click Edit at the top of the page.

4. Next to Audio Conferencing, click Edit.

5. In the Audio Conferencing pane, enable or disable Dial-in callers can be the first person in a meeting.

6. Click Apply.

Source: https://docs.microsoft.com/en-us/microsoftteams/start-an-audio-conference-over-the-phone-without-a-pin-in-teams