I use a microfibre pouch meant for sunglasses or glasses.....it keeps my iPhone XS safe from scratches or dust and accumulated crud when it's in my purse or pocket and fits easily over the Apple silicone or leather case. At home I keep my iPhones naked, only putting the case on when going out, but there are times when I've just used the microfibre pouch, too. I've been doing this for years and it really does protect the phone's screen. You can get these microfibre pouches at places like REI or other places which sell outdoor camping supplies, clothing, etc.
https://www.rei.com/search?q=sunglasses+microfibre+pouch