Connect iPhone to Wi‑Fi
Ensure iPhone has enough battery or plug it into power
Open Settings
Tap your name
Tap iCloud
Tap iCloud Backup
Turn on iCloud Backup
Tap Back Up Now
Keep iPhone connected to Wi‑Fi and power until the backup finishes
To check backup status: Settings → your name → iCloud → iCloud Backup → Back Up Now (and review the timestamp)
To back up to a computer (macOS Catalina or later): connect iPhone to Mac with a cable
Open Finder
Select your iPhone in Finder
Under Backups, select Back up all of the data on your iPhone to this Mac
(Optional) Check Encrypt local backup and set a password
Click Back Up Now
To back up to a computer (Windows or older macOS): connect iPhone to PC with a cable
Open iTunes
Select the iPhone in iTunes
Under Backups, select This Computer
(Optional) Check Encrypt iPhone backup and set a password
Click Back Up Now
To verify the local backup: review the backup list in Finder/iTunes (based on the device and date/time)