@Allie Zhang, Thanks for posting in Q&A. For the device which is enrolled with Automated device enrollment (supervised). There's a setting named "Block removing apps" which can prevent removing app. Please confirm with your Intune admin to see if we have set this.
https://learn.microsoft.com/en-us/mem/intune/configuration/device-restrictions-ios
If the above setting is not set, to remove a device in Intune in company portal, firstly, you can check if the device is in company portal or its website and then remove it.
https://learn.microsoft.com/en-us/mem/intune/user-help/unenroll-your-device-from-intune-ios
https://learn.microsoft.com/en-us/mem/intune/user-help/remove-your-device-cpwebsite
Then you can see if any management profile still existing, if yes, remove it.
https://support.apple.com/en-sg/guide/iphone/iph6c493b19/ios
Note: Non-Microsoft link, just for the reference.
At last, touch and hold on the company portal app and then remove the app.
Hope the above information can help.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.