How Do I Mark iPhone voicemails new after listening to them?

I receive a lot of calls and voicemails everyday. Sometimes I listen to a voicemail, but can't address it right away. How do I mark it so the badge remains on the phone icon on my home screen? I need a reminder that there is a voicemail that I still need to return.

The same question with missed calls. Sometimes I want to see who I missed but don't want to call them back right away. How do I leave the badge on as a reminder?