On the other hand, if you want to replace the app icon with your own image -- or you don't have iOS 18 -- you'll have to use the Shortcuts app. How to customize an app's icon using the Shortcuts app ...

To make a call on the WhatsApp mobile app, go to the contact you wish to call. In the top right-hand corner, you’ll see icons for phone and video. Tap on the one you want to use.