When detected as a conference call that can be joined via a swipe, the icon will appear with a phone image overlay.
To join the call, swipe right. Swiping left will dismiss the meeting from the screen.
If you are looking for the ability to join other conferencing solutions or other options to join the call (ex. by using the app instead of the phone), please make your voice heard and vote on those ideas here:
More Conferencing Solution Support:
Join a Conference Call via the App
The Next Lock Screen Team