>>714148321
Catti being the person on the phone is a good theory, and it helps navigate a possible problem with some other candidates (ellipses in the phone call could be words the soul didn't overhear).
Something I don't see discussed much is Carol having a corkboard in her room, something Asgore's implied to share which given the leniency she's been granting to him makes me skeptical about her being the knight (The Black Shard conversation Asgore has that you can eavesdrop on)