Here are the step you need to take to change your settings in your iPhone for your
“Deleted Items, Sent Items…etc., to go the iPhone folders or on the server.

NOTE: Make sure you’re on the latest iOS update for you iPhone.

1. On your iPhone, click the “Settings” icon.

2. Click on Mail, then “Mail Accounts“.  (Note: if you’re on iOS18, you’ll need to select APPS first.)

3. Under the “Accounts” section, select your email account.

4. Click on your Email address at the top that you want to manage, you’ll be taken to another page.

5. At the bottom you’ll see the “Advanced” section, tap on the “Advanced” section.

6. You’ll then see the following folders under the “Mailbox Behaviors” section, for this example, you’ll select “Deleted Mailbox“.

7. You’ll see the option for “On My iPhone” then below “On the Server“.
There you will choose if you want your deleted email to either go to the “Trash” folder on your iPhone
or if you want it to go “Trash” or “Deleted Items” folder on the server.

8. After you’ve made your selection, click the “Advanced” link at the top left hand corner of your screen to see “Mailbox Behaviors” section, then click the “Account” link at the top left hand corner.
Then click the “Done” at the top right hand corner.

9. You have successfully updated your settings for that folder on your iPhone.