Voicemail/Greeting

I have an iPhone 14 Pro Max and I have/had a saved custom greeting. Now, I’m going insane looking for answers. It keeps going back to “default” and will not give me the option to save my “custom” greeting. I have to have my “custom” one set because I have cancer and the radiation pretty much makes it impossible for me to speak for long periods of time. So, in my “custom” greeting, I explain that text messages are better than voicemail because of that. I have looked everywhere to figure it out and I can’t find anything. I’m also new to this service, so bare with me if this answer has already been asked. Thank you in advance community! I’m going nuts trying to figure it out! 🤪 🙏