Do this by tapping the grey gear icon on one of your iPhone's Home screens (the Settings app may be in a folder entitled "Utilities").;
,,, Your contacts will rearrange to reflect their last names in alphabetical order.


If there's already a checkmark next to Last, First, your contacts are already being sorted by their last names.
Open your iPhone's Settings.
Scroll to the fifth group of options and select Contacts.

,
Tap Sort Order.

,
Select Last, First.
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