Audio Conferencing in Office 365 lets users call in to meetings from their phones. Audio Conferencing allows up to 250 phone attendees.
Calling in (dialing in) to meetings is very useful for users who are on the road and can't attend a meeting using the Skype for Business or Microsoft Teams app on their laptops or mobile devices. But there are other scenarios in which using a phone to attend a Skype for Business or Microsoft Teams meeting can be a better option than using an app on a computer:
Paid in addition to an Office 365 license, monthly commitment