@Dhaval Dattani Thanks for posting in our Q&A.
To clarify this issue, could you successfully remove the management profile in Settings > General > Device Management? If yes, after removing the profile, the device is not managed.
If not, it seems that the iphone is ADE enrollment and IT configured he setting "Locked enrollment" to "Yes" in the Apple enrollment profile, so we can't remove MDM management profile manually in the iPhone.
https://learn.microsoft.com/en-us/mem/intune/enrollment/device-enrollment-program-enroll-ios#create-an-apple-enrollment-profile
Given this situation, it is suggested to contact the IT in the old organization to delete the iphone.
If there is anything update, feel free to let us know.
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