While I know that the prevailing theories about the Phone Voice right now are that it's the Knight or at the least Carol, in a conversation last night I was jolted to a new consideration that I'm feeling pretty gobsmacked by the thought of:
What if that voice is Ralsei, calling from the Dark? Hence the noise-- it's not exactly garbage noise, but it's distorted, with darkness as it's text box.
Honestly my biggest piece of consideration for all of this is:
Everyone has been using this to suggest the voice is Carol, because she shows up shortly after this phone call. But here's the thing: She shows up even if Kris doesn't call her. In the Weird Route, Kris is raging against the soul for whatever it did to Noelle. There is No Way they called Carol between whatever ultimately befell Noelle and Carol arriving home. She was going to come home early regardless of our or Kris' actions.
I propose instead that this was Ralsei saying the he will be right there, at the Sanctuary. He is ALREADY there when Susie and Kris arrive. We know that in the kitchen the voice mentions the fountain at the church, so for Kris, "there" is not ambiguous, while to us as the Soul audience it is vague, and we're tricked to use recency bias.
Additionally, this lets us further add meaning to the closed eyes scenes in previous chapters, where Ralsei is telling Kris something outside of the knowledge the Soul is given.
Has Ralsei been explaining pieces of the prophecy to Kris without the Soul present? Or maybe just been counseling Kris on what the Soul needs to do next? Or what Ralsei needs next alongside Kris? Kris doesn't hate Ralsei-- every option especially in Chapter 4 to be mean to Ralsei results in Kris maliciously complying to the will of the Soul, mumbling, covering their mouth, keeping their mouth shut, etc-- so if whatever Ralsei was telling Kris in these scenes was upsetting, we would know by how they allow the Soul's choices to come through.
Ralsei also tends to use Kris' name A LOT when he speaks to them directly. He does the same with Susie, too, but I think it's a very specific character voicing choice to establish that he uses Kris' name almost every single time he begins dialogue with Kris. I combed through Chapter 1 text data and every time that Ralsei begins talking specifically to Kris, their name is used somewhere near the beginning of the interaction. Likewise, the voice in the phone uses Kris' name A LOT. This isn't something people normally do when talking directly to a person, but it is an established verbal quirk of Ralsei's.
It begs the question, though, what is the promise Ralsei would be referring to? Why would Ralsei call specifically when he does at the end of Chapter 4 to say specifically what he does? And to the counter point, why would Carol or the Knight call Kris that late just to say "don't forget .... You promised"?
There's 2-3 more chapters to learn about this, and I could be heavily overlooking some key details, but part of the joy and beauty of being on the release floor of thjs game is not knowing what pieces are important yet! Would love to hear from others if this speaks to you or you have any further considerations on it!