There might be a setting somewhere (there used to be in the past but not sure now) in your phone's email client that is something similar to "when deleting email, leave data on server". It probably also depends on the email type, too, like corporate email or Gmail or any other flavors of email. It seems like my sbcglobal (Yahoo) account had that setting, but not sure now.
Maybe someone else will chime in with a better suggestion.
I did as you suggested as it worked for my Shaw account, but I had no luck finding any setting for my gmail account. Thanks for your help!Have you checked in the webmail version (if available) of your email account? Sometimes the setting is only there vs. on the PC program or phone app. Other than that, it might not be possible.