Connect your iPhone to your Mac with a USB cable
Open Finder on your Mac
Select your iPhone in the Finder sidebar
Click Trust on your iPhone if prompted
Click Trust on your Mac if prompted
In the General tab, select Back up all of the data on your iPhone to this Mac
Optional: check Encrypt local backup
Click Back Up Now
Wait for the backup to finish
Confirm the latest backup time in Finder
Eject your iPhone safely when done