Make sure that you set up your voicemail. To check, dial your own phone number from your iPhone and leave yourself a message. Call your iPhone from another phone and try to leave yourself a voicemail. Go to the keypad and press and hold on the 1, or press the Call Voicemail button. This dials voicemail. Check if you have any missed messages.
Enter a name for the new greeting and then tap Save. Change your greeting. To use a greeting that you've already recorded or switch back to the default greeting: On your iPhone or iPad, open the Voice app . At the top left, tap Menu Settings. In the Voicemail section, tap Voicemail greeting.

The telephone systems have the feature named as Voicemail. VoIP is the best example of it. When a receiver is unable to pick up the phone, then the caller can leave the voice message on the receiver’s phone. In older telephonic machines, such messages were stored as a voice message directly, and the receiver can hear them later. In modern telephone systems, such info is being stored on the server of the service provider in the user’s mailbox. It is similar to email in which the messages are saved in the form of audio instead of text.
Step 1. Tap the phone app from your home screen. It’s the green icon with the white-colored phone in the middle.