How to clear phone app data on S7 with Marshmallow

[AC Question]

My Galaxy S7 has a voicemail notification that will not go away (despite not actually having any new voicemail). From past experience with this problem, I know that the way to fix this is to go into Settings>Applications>Phone>Clear Data. However, suddenly I can no longer clear data on the Phone app. I understand that for other apps I now have to go into Storage to find Clear Data and Clear Cache, but now there is no Storage option on the Phone app like there is for the other apps. I have looked everywhere in the settings and in the Phone app for a way to do this and I can't figure it out. I cleared the cache for all apps and it didn't help. Clearing the cache and data for the Voicemail app doesn't help, either. How do I clear data for the Phone app and/or get rid of this annoying new voicemail notification? Thank you.