How to resolve iPhone 17's 2-Step Verification process showing an unknown device?

The name of your Device is listed at Settings > General > About > Name, and it is easy to change.

Also note that a Model Identifier of a device is completely different than the type of the device you have, so not sure where you are seeing the iPhone 18 being listed and whether that is showing the Model Identifier or name of the device you have listed in Settings.

• iPhone18,1 = iPhone 17 Pro
• iPhone18,2 = iPhone 17 Pro Max
• iPhone18,3 = iPhone 17
• iPhone18,4 = iPhone Air

If you have a screenshot of where you are seeing this it may be helpful, as long as it does not reveal any personal information.

research4f wrote:

But it asks if I trust an iPhone 18 not an iPhone 17.

Apple has never released any device called iPhone 18.

It sounds like some unauthorized person has at some time accessed your Apple Account.

If you think your Apple Account has been compromised - Apple Support

UPDATE: Mac Jim ID’s comment regarding your device name does apply. Might you have mistakenly named some device “iPhone 18”?

I wonder if the passkey is or was identifying your iPhone by Apple’s internal model number 18.x For example Apple refers internally to iPhone 17 Pro Max with model identifier 18.2. I’ve seen this in other highly secure apps such as financial and banking apps.

research4f wrote:

Is [if] the process to change phone name laborious && time consuming?

No, it’s trivial.

Settings > General > About > Name > [change the name].

Of course, that must be done on the device whose name is to be changed.

research4f wrote:

if the process to change phone name laborious && time consuming? If so I’ll allow time before I do it.

As I am late to the party, I will just add this. Be sure to back out using the arrow in the upper left of the screen once you've changed the name. If you just leave Settings, it may not take.