Bob uses an IoC feed to allow his SIEM to identify and correlate common malicious activity. What phase of the incident response process best describes this?

The detection and analysis phases of the incident response process both commonly leverage IoCs to detect and then correlate information to identify incidents. Preparation might involve setting up threat feeds and building automations to help notify security administrators of issues. Containment and eradication may leverage threat data to help understand common actions taken by threat actors, but the SIEM detecting and correlating events is not typically part of containment or eradication.