The following instructions are for DNSCloak on iOS. DNSCloak is recommended for iPhones with a supervised child account for which you would like to lock the DNS setting with a passcode.
For all other iPhone users the recommended setup is DNS over HTTPS directly in iOS.
Take your DNS over HTTPS configuration info (click or tap it to copy for easy pasting):
In DNSCloak, click edit to get into your configuration.
Go to the bottom and paste the configuration you copied in Step 1. Then tap the check mark to save and go back to the main screen.
Pick blockerDNS from the list of servers and then choose Use this server.
If you're connected correctly, the "play" button (triangle) should change to a "stop" button (square). You're done!