How do you get iOS 14 beta off your phone?

turingtest2 provides this reply in: How i can removed ios 14 beta and install… - Apple Community

"From the link posted above:

Remove the public beta by deleting the beta profile

The easiest way to remove the public beta is to delete the beta profile, then wait for the next software update. Here's what to do: 

1. Go to Settings > General, and tap Profiles & Device Management.
2. Tap the iOS Beta Software Profile.
3. Tap Remove Profile, then restart your device.

When the next public version of iOS is available, install it to move back to a non-beta version of iOS. If an update is already available, you can install it by going to Settings > General > Software Update, but the iOS version must be later than the version you have.

If you don't want to wait for a software update to install a non-beta version of iOS, follow the steps to restore iOS.

If you've already employed steps 1 through 3 then you may simply have to wait for the next update.

tt2"

How to uninstall iOS beta software - Apple Support provides instructions.

Didn't you read the instructions when you installed the Beta?

Read here => How to uninstall iOS beta software - Apple Support