SCRATCHES are not even close to being a common problem. CRACKING is. We need glass that is resistant to shock and won't spiderweb when dropped. Current smart phone and tablet screens are already fairly resistant to scratches; I don't use a screen protector on my iPhone and I certainly don't baby it yet there are no easily visible scratches.
Why do you assume it's for a phone? If this was for an iWatch, Apple wouldn't need to design a drop-proof device if it's attached or worn, rather than held.