can i exchange my damaged iphone

Take a look at his for repair options and pricing. I don’t think Apple will replace the back glass. They will offer an out of warranty replacement for a price.

iPhone Repair - Official Apple Support

If the back glass is broken, I’m not sure that you can get anything on a trade.

in addition to that advice and to save a trip, if you go to the apple trade-in site (google for the one in your country) and if you answer truthfully about the back it will tell you to recycle it.

I tried for someone else.