Webroot has effectively shut down O365 for my whole organization by blocking the login page.

It doesn’t matter which way we approach, eg. “portal.office365”, “portal.azure” it’s when you get to the login landing you are met with:

Warning: This is a High Risk Site
Webroot has blocked the website you are trying to access for your protection:
https://login.microsoftonline...
Detected Phishing Site
This site might try to trick you into disclosing your login, password, or other sensitive information by disguising itself as a website that you trust.