When searching for an app on my iPhone I get a black, blank screen
From Use Search on your iPhone, iPad, or iPod touch

Swipe to search

Swipe down from the middle of the Home screen.
Tap the Search field, then enter what you're looking for. As you type, Search updates results in real time.
To see more results, tap Show More or search directly in an app by tapping Search in App.
Tap a search result to open it.


Emphasis added by me on step 1.

If the above default method is not working for you, then restart the iPhone and see if the issue persists.