How to delete multiple contacts at once from your iPhone

1. Download the Groups app on your iPhone.
2. Launch the Groups app on your iPhone.
3. Grant Groups access to your contacts when prompted.
4. Select All Contacts from the Groups list.
5. Go through your contacts and mark the ones you'd like to delete by tapping on the circle outline to the left of their name.
6. Tap Choose Action at the top.
   
   
7. Tap on Delete contacts... in the popup menu.
8. Tap on Remove from my iPhone! in order to confirm.
   

That's it! You should now be able to hop back into the built-in Phone or Contacts app and verify that the selected contacts were in fact deleted. While Groups isn't the most attractive app available, it gets the job done quickly and efficiently. Give it a try and let me know how it worked for you!