Website: https://techboomers.com/t/record-change-android-phone-voicemail-greeting
Arguably the most intimidating factor when leaving a voice mail is the fact that once you leave the message, "in one take," there is no taking it back. That is why, especially in the business world, an overwhelming amount of people revert to email rather than leaving a voice mail message. Especially in a technologically advanced world, email or text messages are now used as a primary form of communication. Although there is a good argument behind opting for the written word over the spoken one, an email can lack the human touch, the emotion and enthusiasm in a voice, that can often times generate a better response. In fact, there is no impact that compares to delivering a clear, concise, professional message through your own unique human voice.

Note: If necessary, delete an existing greeting (limit of 2 greetings) to make room for the new greeting: Tap the Menu key, tap Delete greetings, tap the check box next to the desired greeting, and then tap Delete. Tap the Record icon to record your greeting. Tap the Stop recording icon to stop recording.
5. Hit “Record” on Audacity. Then, on your phone, play the voicemail you’d like to record. When your message is done, stop recording. If you want to get really fancy, you can use Audacity to chop off any dead air at the start or end of your recording.