How to configure Apple Mail on iPhone XR (iOS 12.4) to download emails from mailserver but not delete them on it? I keep my mailfile on my laptop which uses a mail client to download and send email through my mailserver. When I download email it is then deleted from the server. I can also read and send mail using webmail access to the same server, but when I read it using that method it is not then deleted - it is only deleted later when I download it using my mail client. The mailfile is backed up but not synced, and nowhere is the cloud involved.

Obviously I can read and send mail from my iPhone using a web browser such as Safari.

My question is whether I can also configure Apple Mail to download mail from the server such that it is not then deleted on the server. The reason I ask is that I would sometimes like to read emails on my iPhone before I have downloaded them on the laptop. I would then eventually delete them by hand on the iPhone because they would later get downloaded and filed in the usual way on my laptop. But of course they can only get downloaded to the laptop so long as the contact with the server using Apple Mail doesn't cause them to be deleted on the server.

I suspect the answer is "No - if you want to handle your mail that way, then when you read it on your iPhone your should only use webmail access through a web browser". I may be wrong, though.
Sure. Have Apple mail client use IMAP protocol to leave a copy on the server and just don’t delete on iOS. 

Next time your machine deletes things off the server, the next IMAP sync will clean up things on the iPhone automagically.