Hi Ann,
Thanks for reaching out. I understand how frustrating it is to keep getting spam calendar invites in Outlook for iOS.
Unfortunately, you can’t completely block them, but you can reduce them. Open the Outlook app, go to Calendar, select the spam event, tap Decline, and choose Delete and Decline if prompted. If they keep appearing, check iOS Settings > Calendar > Accounts for any unfamiliar subscribed calendars and remove them. You can also block the sender and report the invite as Junk or Phishing in Outlook.
Do these invites show up only in Outlook or also in your iPhone’s native calendar?
Let me know how it goes. I will be more than happy to assist you.
Regards,
Carlo