According to NIST SP800-61, the incident response phase called "Containment, Eradication, and Recovery" involves containing the incident, eradicating the threat, and recovering from the incident2. In the scenario described, the engineer worked on containing the DDoS attack by identifying the attacker and the technique used, which is part of the containment process. The recommendation to implement Blackhole filtering is part of the eradication process, where measures are taken to prevent the attack from happening again. Finally, restoring the server is part of the recovery process, where normal operations are resumed. Therefore, the engineer finished work during the "Containment, Eradication, and Recovery" phase. References: NIST SP800-
61 Computer Security Incident Handling Guide2.

The weaponization step in the Cyber Kill Chain model involves creating or repurposing malware based on the information gathered during reconnaissance to exploit vulnerabilities in the target's system. This step culminates in the preparation of the malware to be delivered to the victim2.
Understanding Cisco Cybersecurity Operations Fundamentals (CBROPS)
Cyber Kill Chain

Explanation:
Exploitation - The targeted Environment is taken advantage of triggering the threat actor's code Installation - Backdoor is placed on the victim system allowing the threat actor to maintain the persistence.
Command and Control - An outbound connection is established to an Internet-based controller server.
Actions and Objectives - The threat actor takes actions to violate data integrity and availability