Remove the delete/archive button from iPhone email
That’s unfortunately part of the UI and you cannot remove the button.

Post feedback to Apple at https:/apple.com/feedback
Use a different  Mail client

I personally got tired of the limitations and idiosyncrasies of Apple’s mail and calendar applications (similar to this) and switched to Outlook.  There are many 3rd party apps; you may find one you’re more in tune with.  From what I understand, iOS/iPadOS 14 will allow you to set your own default mail, calendar and browser breaking from the built in apps.