Using my ISP's email. Is there a setting for when I delete mail to keep it on the server? All mail I delete on my phone is deleted from my email server also at the same time.
If deleting mail on your phone deletes it from the server then your Outlook settings are completely irrelevant. You need to find another mail app that gives you that option.
If adjusting Outlook settings did fix your problem then you misstated in your OP.