Hello brucewaldron
Thank you for participating in the Microsoft Community, My name is Miguel T. I'm an independent Advisor
When you instruct iOS Mail to move a spam email to the Junk folder, it does just that, as long as it knows about the account's spam folder as it does for iCloud Mail, Gmail, Outlook Mail, and some others. If the Junk folder does not exist in the account, iOS Mail creates it.
The effect of moving messages from the inbox or any other folder to the Junk folder depends on how your email service interprets the action. Most common email services treat messages you move to the Junk folder as a signal to update their spam filter to identify similar messages in the future, but sometimes they are not.
Spam filters aren't perfect. If you end up receiving spam email in the iOS Mail app even after you mark the sender or email address as Junk, the best solution is to block the sender entirely. Tap Settings > Messages > Blocked > Add New and then type or paste in the sender's email address to block all email from that address.
Or another workaround is go to your account directly from the web and make the process of spam filter from there, IOS Mail App will reproduce the same change that you previously did on Web
I hope this information has been useful, please let me know if you still need assistance.