If my iCloud is locked, how can I remove it from my iPhone?

First try this

Follow the onscreen steps to enter the Apple ID and password you used to set up your device or your device passcode. If you don't remember your Apple ID, try to sign in with an email address or phone number that you regularly use for Apple services.

Learn how to find your Apple ID or reset your Apple ID password.

Remove Activation Lock on the web if a device is offline

1. Go to www.iCloud.com/find.
2. Sign in with your Apple ID, email address or phone number, and enter your password.
3. Select the device that you want to remove from iCloud.
4. Click Remove from Account.

If you're the original owner of the iPhone and cannot remove the lock with your Apple ID credentials and can provide valid proof of purchase information you can start an Activation Lock support request.