Can I receive calls on whatsapp if my storage is full?

No, you’re going to find a lot of apps issue warnings, crash, lose data and otherwise malfunction if your device’s storage is full. You need to delete things to free up space. Just like your computer needs some free hard drive space for cache and temp files, your iOS device needs space for those things as well.

The app must have storage space on the iPhone to function properly.

Besides if the storage space on your iPhone is that low, you stand a good chance of other apps not functioning correctly and/or corrupting everything on your iPhone. You should make every effort to delete enough data to free up storage.