1. Make sure your phone is connected to Wi-Fi

2. Go to Settings > [your name],  
and tap iCloud. 

3. Tap iCloud Backup

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4. Tap Back Up Now. Stay Connected to your Wi-Fi network until  the process completes.

5. Make sure that the backup is finished: 

1.Got to settings  
2 Click [your name]
3. iCloud
4.     iCloud Storage
5.Manage Storage
6.The Select your device 

The backup should appear in the details with the time and backup size. 

Get help backing up your device with iCloud Backup:         
https://support.apple.com/en-us/ht203516