There are times where you need to join a Microsoft Teams meeting, but you’ve forgotten your headset, or maybe the battery has run out. Frustrating!
You might be tempted to just use the builtin microphone and speakers on your laptop. However, if you are in an open office, no one else wants to hear your meeting! Even if you do manage to find a quiet space, using internal components is just so bad for audio quality that you should explore better options.
If you are enabled for Audio Conferencing dial out by your IT administrator you can connect your mobile phone to the Teams meeting as an external microphone and speaker. This way you can continue to participate in the meeting, share your video, share your screen and see others presenting, whilst using your mobile to listen and speak.
You can do this in the pre-meeting join screen in the Teams client, by pressing Phone Audio

Enter your mobile number and press Call ME

Answer the incoming call to your phone and you will be instantly connected to the meeting.
If you get disconnected on your mobile, you can quickly reconnect the call by clicking on the ellipsis (…) in the meeting controls bar and choose Show Call Details
From the Call Details blade you will notice your mobile number is already entered and you can click Call Me to reconnect without leaving the meeting and rejoining.

Participants will know you are connected via external audio if they view your account in the meeting participants blade with a person with a telephone icon

If this is shown, meeting presenters cannot mute you, you control your muting and unmuting using the call controls on your mobile device.