If WiFi is not available is there another way to back up my phone?

IOS 15 + a 5G iPhone will allow you backup on a cellular connection, however, that is not applicable here. You do not have a computer and do not have Wi-Fi. You have an iPhone 11.

1. Will borrowing a computer from a family member or a friend help? Probably not if you want to periodically create backups. If you want to immediately use that backup to restore this iPhone or another, then it may be helpful.
2. If, creating an iPhone backup on iCloud is the ultimate goal, then you can do it from McDonalds or another Starbucks or some similar business. They have Wi-Fi Networks that you can use and you can create your backup. Apple Store, if there is one near you, is another option. For that matter, a friend’s Wi-Fi Network will also work.

Axel F.

Go somewhere where you can access Wifi would be your only choice if you don't have a computer.

You can connect your device to a computer to back up.