Open the Phone app
Tap Voicemail
Listen to each voicemail
Delete each voicemail after listening
If your carrier supports visual voicemail, press and hold a voicemail and tap Delete
If there is a trash or delete icon, tap it
To clear all voicemails, open the Voicemail tab and delete them one by one
If voicemails remain on the carrier side, call your voicemail inbox and follow the prompts to delete messages
If needed, contact your mobile carrier for voicemail deletion options