When dialing out to a PSTN number from a Teams meeting using Audio Conferencing, 'remove participant' only becomes available if the call connects, either by someone answering their phone or it going to voicemail.

If nobody answers the call or you have dialed wrong, you cannot cancel it before it is answered and it stays as 'calling'.

The only way to cancel the call is to end the meeting which is inconvenient if other participants have joined successfully.