Connect your iPhone to your Mac with a USB or USB-C cable
Open Finder on your Mac
Select your iPhone in the Finder sidebar
Click Trust on your iPhone if prompted
Click General in the Finder window
Select Back up all of the data on your iPhone to this Mac
Optional: check Encrypt local backup to save passwords and Health data
Click Back Up Now
Wait for the backup to finish
Confirm the latest backup time in Finder
To back up with iTunes on older Macs, open iTunes, select your iPhone, and click Back Up Now