I suspect you may have a hotmail, outlook, or other Microsoft exchange account. If that is the case, their servers have once again been swamped with spam calendar events. The Calendar app on your phone simply syncs the events that are on those servers. This is not the first time Microsoft has had a problem with these.
If you do not use the calendar for that email account you are using, then you just need to stop syncing the Calendar for that account and they will go away. Just stick with the iCloud calendar and you should have no problem. When people add the mail accounts, they don't realize that they are also adding the calendar or contacts associated with the email. You can view what those accounts are syncing by going into settings and choose the Calendar. You don't want to remove the account, just flip the switch for syncing the calendar on that account.
