Speakerphone button disappearing if I open another app

[Wayne de who]

I am on hold a lot, so I always put the speaker on.  If I open another app there is no way to turn off the speaker button.  There wasn't a way to even hang up, but I found you can set the Side Button as the hang up.  But once you leave your call screen there is no way to go back to that screen.   What am I missing?

[Mobz]

That's weird. There's usually the ongoing notification in the notification bar...?