how to completely remove app from iphone

With iOS 14, 3rd party apps and some Apple apps can be either deleted or moved to the App Library. See: instructions in How to delete apps on your iPhone, iPad, and iPod touch - Apple Support

If you are asking about a built-in Apple app, see: Delete built-in Apple apps from the Home screen on your iOS 14 or iPadOS device or Apple Watch - Apple Support

No, the app is in the cloud in the App Store, not in your storage. If you go to the App Store and it says "Open" it is still on your iPhone somewhere. If it shows the cloud symbol when you tap it then it will download a new version and install it. If it still is causing a problem contact the developer.

Press and hold the app, when they all start shaking tap the x in a circle at the top left of the app.