Real-time Anti-phishing is part of the Advanced Security package and protects you from the threat of phishing emails. If you click on a link in an email that's suspected to be phishing, you'll receive a warning and you'll be asked you if you want to proceed. If you decide to proceed the link will be scanned. If its determined to be phishing you will receive a warning but can still proceed with caution. If its determined to not be phishing you'll be taken directly to the link.

Tip: You can change your level of anti-phishing protection in Settings. Click the gear icon in the top right and select "All settings" from the dropdown menu. Under Mail, click Anti-Phishing. You can select your level of protection here.