When I change screens while on a call I can't go back to the call screen to finish it on my iPhone XS Max

17.1.2 IOS version

freuently when I. Am on a call and switch screens: like go to my contacts to share information with they party I a talking to I will stay on the line verbally with them but when we want to end the call my phone does not give me the screen with the red button oo I can hang up. So we stay connected verbally and I cannot disconnect the call.

[Re-Titled by Moderator]