Hacking

You can remove those devices in Settings -> Apple ID on your iPhone, iPad or Mac or in iCloud.com/Settings.

Where and how did the iPhone shows devices you don't have?

Those could be old devices you once owned or used at iCloud.

There's no device shown in iCloud settings.

If you have Family Sharing then it is in

Settings > [your name] > scroll down to see device using your Apple ID.