I have a red bell that keeps popping up on my phone

The red bell with the slash thru it is showing on my iPhone. I have gone into focus & notifications, but am still missing sound notifications

Depends on phone. My control center (iPhone SE3) pulls up from bottom of screen.

It could also be the toggle switch for ‘silence’ is on. On some models it’s hard to see the position, depending on what case you may have. Mine is just above the volume rockers on the left side. Flick it back and forth to see if the bell pops up.

That means you have muted your phone. From the top right hand corner of the phone slide down to open Control Center and see the bell icon and tap it to unmute your phone.