Once done recording, go to the Voicemail greeting to find all the recorded voicemails. Click on the "Play" button beside the name of the voicemail to play it. To change the name of the recording, tap on it, and enter the name of someone who called you and set it as active. The caller will hear the voicemail greetings once they called you.
Website: https://docs.microsoft.com/en-us/microsoftteams/set-up-phone-system-voicemail

There are two steps you have to do before you can use voicemail on your phone. The first is that you have to add a voicemail number. This number varies by country and also your service provider. If you’e use AT&T, you can follow AT&T Galaxy S21 voicemail setting. Open the “Phone” app. Tap the 3 dots on the top right. Tap “Settings“. Tap “Voicemail“. Tap “Voicemail Settings“. Take note of the green number below “Voicemail number“. Go back to the dialer and enter the number from Step 6 (including the *). Press the green phone button. The voicemail number has been set. Return to the Start screen.
A busy greeting should tell callers that your phone lines are currently in use. You can direct people to wait on hold or leave a message. For example, “Hello, you’ve reached [company name]. Our representatives are currently helping other customers. Please stay on the line to speak with the next available team member, or press one to leave a message and we’ll call you back.”