How to stop email spam on iPhone?

One way to filter SPAM out of your main inbox, is to send it to the junk folder.

To send an email to the junk folder on the Apple Mail app you can follow the instructions in this article:

Identify and filter junk mail in iCloud - Apple Support

To block a specific email address or phone number from contacting you refer to this article:

Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch - Apple Support