IOS 15
Downloaded IOS 15 why it’s refusing to install in my phone?
iPhone 6s, iOS 13
I had that problem as well. I had about 30Gb out of 32Gb full on the iPhone. I Offloaded several larger apps to get the usage down to less than 25Gb (freeing up at least 5Gb) and then it installed.
Check your iPhone Storage.
Settings > General > iPhone Storage
If you don’t have at least 5Gb free (I am guessing at the amount needed), try offloading some apps and try the install again.