The large icon is the Clock widget; the smaller one is the Clock App.
Apps can be removed from the home screen without being deleted. Go to the App Library (swipe left past your last home screen). From there you can touch and hold an app and slide it left back to the home screen.
Also note the Search window at the top of the App Library.
If the Clock app was deleted, see the following from Delete built-in Apple apps from your iPhone, iPad, or Apple Watch - Apple Support
Restore a built-in app that you deleted
- On your iPhone, iPad, or Apple Watch, go to the App Store.
- Search for the app. Make sure that you use the exact name of the app.
- Tap the Redownload button .
- Wait for the app to restore, then open it from your Home Screen.
The following has information about removing the widget if you want to do that: How to add and edit widgets on your iPhone - Apple Support