On desktop (MacOS and Windows) or on Wire for Web:
When receiving an incoming call while in Wire, click ACCEPT to answer it or DECLINE to ignore it.
If Wire is minimized, an incoming call notification appears. Click the notification and inside Wire click ACCEPT to answer it or DECLINE to ignore it. You will no longer hear ringing, and the call visual will disappear.
For instructions on how to do this on mobile, click here.