Undocumented feature (I think)

In addition to the useful information provided by my friend ProustGiulio, try these steps Go to Settings > accessibility > Display & Text Size > Larger Text- Turn off Larger Accessibility Sizes.

If it's already off and still having the same problem, go to Settings > accessibility > in the last page tap on Per-App Settings > Choose the app where this issue appears > Larger Text > Reset Font Size to Default.

Try a "forced" restart of your iPhone, using these instructions:--> Force restart iPhone – Apple Support

If the issue persists, and if you're sure that nothing (cover, screen protector, dirt, scratch) is interfering with your touch screen, it might be a hardware (screen? other internal component?) glitch, but we, just users like you, cannot diagnose that issue remotely, sorry.

I suggest that you make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

Hey there,

To turn off Zoom, go to Settings > Accessibility > Zoom, then tap to turn Zoom off.

If you can't access Settings because your Home screen icons are magnified, double tap with three fingers on the display to zoom out.

See ☞ If your Home screen icons are magnified on your iPhone, iPad, or iPod touch - Apple Support

if the zoom is already turned off and you still see that “gray box” please provide a screenshot!