Open Phone → Make sure you are on Keypad → Press and hold the number 1 for a few seconds. It will call your voicemail; You can check your voicemails here. 3. Force close and reopen the Phone app. To force close Phone, on iPhone X and later swipe up until you see the apps in task view, then swipe up again on Phone.
The default, generic voicemail greeting that comes with your iPhone is fine but also rather bland and boring. You can personalize the voicemail greeting on iPhone by recording your own custom version of it. This is a tutorial on how to create a custom iPhone Voicemail greeting.

If your business is closing on one of its normal operating days for a holiday, or is dealing with an emergency or unforseen situation, you should update your after hours announcement to avoid confusion.
You can also erase any of your existing recordings associated with your voicemail box. To delete your name recording, unavailable greeting, or temporary greeting: Dial *98 on your OnSIP-registered phone. Enter your voicemail box number. Enter the PIN/password for your voicemail box. Press 0 for voicemail box options. Press 1 for unavailable greeting, 2 for your name, or 3 for temporary greeting. Press 2 to delete the existing recording on file.