True Tone display option gone after updating to iOS 12

Your signature says iPhone 6.

Having updated to iOS12 on my iPhone X, I can confirm the True Tone setting is still on my phone.

Reboot your phone, which is highly recommended after any major update.

On your phone:

Press and quickly release volume up button

Press and quickly release volume down button

Press and keep holding the power button (hold past swipe to shut down) until the Apple Logo appears

Let go and your phone will reboot.

See if True Tone is back after your phone comes back up.

Scott, it never dawned on me to ask you if you've had the screen on your iPhone 8 replaced with an aftermarket screen? If you have, you now know why you've lost the True Tone setting.

You can try making a full backup, restoring to factory settings and setting up as new.

Even though you purchased it from the Verizon Store it wouldn't held to check the model settings and post here. Also, has the screen been replaced on this iPhone?

You can call AppleCare and they can run diagnostics on your iPhone remotely.

Then I'd recommend you back and restore the phone. You might want to restore the phone via your computer and iTunes this time.

Was this a screen installed by Apple?

True Tone is a hardware setting in the iPhone. If during the install the update does not get responses that the display is True Tone capable then the option would not be presented.

If it was installed by another service it is not an original screen. That is why you are not seeing the True Tone option.

Then schedule an appointment at your Apple Store Genius Bar and show it to them.

What about iOS 12.01? Have you installed it yet? If so, is the True Tone option still missing?

What's odd though is that the setting disappeared from his settings. I can see having a hardware issue, but I wouldn't expect the setting to go away on its own? I echo your comment to have the phone looked at.

It may be an indication you have a hardware problem you were not aware of. Have it looked at.

settings>display & brightness

I'm pretty sure Apple would like to hear from you. Call them at 1-800-MY-APPLE and I'm betting you are transferred to an Engineer. In fact you should ask to speak with an Engineer.

I have this problem too, but on iPhone 8 plus. Running iOS 11 Installed a new screen and True Tone was working perfect but the ALS was disabled. Updated to iOS 12 True Tone is disabled (missing) and now the ambient light sensor works good.