How do I reinstall my photo app

As Photos is not an app that can be deleted, it's there on your phone somewhere.

Check that nothing has been restricted in Settings>ScreenTime

Hello Hieromonk,

It sounds like the Photos app on your phone was deleted. You can first make sure that it is not hidden in your App Library and searching for it:

Use Search on your iPhone, iPad, or iPod touch

You can also see if it is hidden in your App Library by going through the library itself:

Organize the Home Screen and App Library on your iPhone

Regards.