My messenger app crashed and froze I can’t even text anyone or open the app to see my messages, but it’s weird because it happened while I was on the phone and I’m still in the call but can’t use the app?

If you can, restart the app in question: Depending on your iPhone model double press the home button (if it has one) or swipe up half way until all your recently used apps appear as a stack of "cards". Swipe up the "card" of the app in question to remove it from the stack.

Then reopen the app by clicking on its icon on the home screen.

If this did not work, restart your iPhone. Press the side button, until "slide to power off" appears. Slide to power off. Then wait a few seconds. Press the side button until the Apple logo appears. Once the phone restarted, try your app agin.

If it still didn't work, I am out of suggestions and you might need to specify, which messenger app you were using to find someone more knowledgable.