How do I fix error while updating voicemail greeting on iPhone?

I was trying to update my voicemail greeting from an outdated one, and received the “apple.mobilephone.error 1035” pop up. I googled and went through EVERY step, including resetting my network settings, and that resulted in me getting the 1034 error. I am fully updated to iOS 18.5, but I should probably update my rather ancient iPhone. Any help? I would REALLY like my greeting to reflect both my married name and a kind but blunt message for the 4+ per day spam loan offers I get called with. Thanks!

[Re-Titled by Moderator]