For many businesses and professionals, your voicemail greeting is going to be the first point-of-contact for your customers. This is especially true for service businesses, who often rely on their voicemail to collect information from interested parties.
The much safer option is to do this with a third-party voice mail system like Google Voice (but the voicemail recordings are limited to 3 minutes). So it's better to have a paid voicemail service, use the Google Voice recording option for incoming calls outlined above, or spring for the paid recorder services like Recordator.

With this method, you don’t need a third-party app. Call the person you want to chat with, then tap the “Add Call” button on your phone’s screen. Dial your own phone number—the one you’re calling from. This will take you to your voicemail. Once your voicemail has started recording, tap the “Merge Calls” button on your screen. Now, you’ll record your phone conversation onto a voicemail message. When you’re done with the call, you can tap the share button to export it to your Mac via Airdrop, to the Voice Memos app, or transfer it via email or text message. The file is recorded as an M4A, so depending on what you want to do with it, you may need to convert it to MP3 before uploading it to other apps.
So as you could see on top is buffering. So I got to wait a minute and then once that's done, I'm going to press custom here. So now when it says to set your outgoing message, I'm going to choose custom here and I could basically press record. I don't have one yet. So if I did, it would allow me to play it and listen to it.