How to Remove your iPhone when it is lost, sold, or given away (thus you don’t have it anymore) from your iCloud Account.
If you’re no longer using iPhone you can remove it from your iCloud account by following the steps below.
When you remove a device set up to use Apple Pay, Apple Pay is disabled for the device, and your cards are removed from the device, even if the iPhone is offline.
Go to Settings on iCloud.com, then look at the My Devices section.
If you don’t see the My Devices section, your account just has access to iCloud web-only features.
To gain access to other iCloud features, set up iCloud on your iOS device or Mac.
In the list of devices, click the iPhone you want to remove.
Click the Delete button next to the iPhone you want to remove. See the picture below. and you’re done!
If you don’t see the Delete button, click “Remove Device” (below the iPhone’s serial or IMEI number).
Apple changes the way to do this all the time. If it does not work then please let us know.