RED DOT

Can you post a screen shot? I was picturing the Messages app, not the phone app. The phone app will show a badge with a count when you have missed calls and/or voicemail. The number will be missed calls+voicemails. So if a caller leaves a message the count will be 2, one for the missed call and one for the voicemail.

Try force-closing the Phone app→Close an app on your iPhone or iPod touch - Apple Support

Did you also tap on the Recents icon to clear the missed calls?

Do you have cellular data turned on? Voicemail needs it to be on to sync voicemail with the network voicemail server.

What app is the red dot on? If it is Messages, have you tapped the “< Filters“ (if any) at the top of the Messages screen?

Open the phone app and take a screenshot of your phone. Crop it as I did this one and just post this so we can see it.

Did you follow the link I posted to force close the phone app?

I have no idea what you are trying to show with the video. What model iPhone do you have?