The phone is durable. It can be damaged as any mobile device can be by being dropped. Being totally honest, the back of the Xr glass is the most likely to be broken glass on the phone. Remember, the phone is glass Front and Back. One drop and it can break. With a case, it's much more secure.
This is again up to you. If you don't want to put anything on your phone to protect it. Just don't. It's a personal choice.
If you're wanting to see the cool color of the phone you bought, buy a clear case and let the color shine through. There are loads of options you can get on Amazon for under $10.