Find my app says I’ve left phone behind when I haven’t how do I fix this problem?

Hello Kazz79,

Thanks for reaching out to us in Apple Support Communities about receiving a notification about a device left behind. We're happy to help by looking into this more! 

The following support article provides some troubleshooting steps to try for this behavior:

Set up and use Notify When Left Behind in the Find My app

You can in this article how to be notified when you leave a device behind. In this case you may have named the device "Phone" and your iPhone is notifying you that it's left behind. You can use the steps in the article to see what device it is and you can choose to rename the device or stop the notification.

Hope this helps.

Best Regards.