Hello,
I am sorry to hear your phone was destroyed but I think you may be misunderstanding what needs to be backed up. When you get a new device, and sign into your iCloud on it, all your iCloud data becomes available on the new device. You shouldn't think of iCloud as a backup service but you don't need to back up your iCloud data every time you get a new device. The recommended backup is your iPhone data that is not stored in iCloud so it can be transferred to the new iPhone since iCloud doesn't store that data off device.
Also, if your phone was destroyed might not be able to manually back it up to your computer if you had not already connected them and approved your iPhone to always trust your computer. I am going to provide info below but am worried it may not actually help.
How to back up your iPhone, iPad, and iPod touch with your Mac - Apple Support
If you can successfully create a backup using your computer this is the process to use that backup to setup the new iPhone.
Use the Finder or iTunes to transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support
I am not sure if you will get this since you are replacing your old iPhone rather than buying a new one outright but you may get access to more iCloud storage temporarily.
Get temporary iCloud storage when you buy a new iPhone or iPad - Apple Support
If you do decide you want to archive some of your iCloud data to reduce the space needed for it this link has information about the different types of data and how to archive/copy it.
Archive or make copies of the information you store in iCloud - Apple Support
I hope this helps.
