Q: Email deleted on IPhone deleted from server

That is how an imap account works.

Delete in one place, deletes in all places.  The point of an imap account is that no matter where or how you access your e-mail, it is the same.

Not entirely sure what you're asking about, here...

If you cannot access mail on your Mac — in general, and not due to the manual or automatic deletion of a message — then here is the general troubleshooting sequence.   Use Connection Doctor to check the settings.  It's likely that there is a misconfiguration here.  Apple has a tool that might be able to tell you what your email settings should be, too.

As for the messages being deleted, that can be something that a POP connection does as messages are read, unless it's been disabled in the configuration of all devices using the email account.  The "delete from server" setting should be located under the advanced settings for the POP account within the iOS Settings for the Mail, Contacts, Calendars.

If you've manually deleted the message and it's stored on the server, then either POP or IMAP will delete the message, and it'll be deleted across all devices — it was stored on and was deleted on the mail server, so it disappears across all devices accessing that account on that mail server.

I've switched to IMAP for most access, and no longer have any POP accounts around.  If your ISP offers it, IMAP has some advantages here.