How do I set up voicemail without a "set up voicemail" button?

I've Googled. Basically, I'm trying to do this for Mom who can't figure out her voicemail set-up. I don't know how she got here, but there's no voicemail. If I call, I receive the message that there's no voicemail set up.

Ok. I'll set it up for her.

Or not, as nothing seems to align with any of the "how to" instructions online. She may actually be correct this time when she says "it won't let me" log in or do this set up.

Call VM. Should be easy, right?

This is the perpetual, silent screen. No voice, no capacity to enable speaker, it just calls the silent void, forever...

Or:

Occasionally this error screen is the outcome of hitting the "call voicemail" button.

Checked her updates. None pending.

Turned the phone on/off, no fix there.

The carrier, Consumer Cellular, walkthrough wants me to hit a "greeting" button. As you can see above, there isn't one.

I've never had an issue setting up my own voicemail on any of my iphones since inception. How do I get this voicemail going?