Those should be your channels.
You can do a ‘core show channels concise’ and see what channels are up and their duration.
Active calls between an endpoint and the PSTN should have two channels, one will be your endpoint (SIP/1051 in this case) and one will be your provider (SIP/Windstream)
I recommend looking for channels with the prefix SIP/1051 if that’s the endpoint that is ringing.