Also, carriers have a limit to how long they'll let you record a voice mail. Test it with your phone and a friend before you trust this method.
Tripboba.com - Voicemail is a voice message that a caller will leave to your mailbox when you’re absent or busy with another conversation. The same goes if you’re trying to call someone else and they don’t answer. You can leave a voice message and they will receive the mail, allowing them to hear what you want to say.

First I would check the phone to see if it saved the greeting to its files. Some phones do and some don’t. If you are unable to find the voicemail greeting file, google the question for your type of phone. If you’re unable to find it or do it, call youe cell phone carrier to see if they can help. Some carriers still save voicemail greetings on their systems. It’s a great reminder though that if you have a greeting you really want to keep, to make sure you record it and save it to your computer and to a flash drive or cloud drive for good measure. Hope that helps! Laura
Tap a message notification. When you get a voicemail, you can check your message from the notification on your phone. Swipe down from the top of the screen. Tap Voicemail . Call your voicemail. You can call your voicemail service to check your messages. Open the Phone app . …