Missing of on call icon

this picture was taken from my iPad for sample. Yet the problem is on my iPhone.

the green phone call icon on the top right was missing on my iPhone when I am in zoom meeting, Microsoft team meeting or on phone call.., and during call I jump to Home Screen and there isn’t the phone call icon is appeared.

it just happens few days, before this happen, it works as normal, it always appear the on call icon while I was jumping to Home Screen.

please kindly guide me how to solve the problem. Thanks