If the individual accessing the system for disaster recovery purposes were not familiar with the IT system and required system administrator logon credentials, what additional step would be required in the recovery phase?

Recovery phase is the last phase in any disaster recovery process.

According to the given situation it is better to call System administrator so that the system is recovered properly which even avoids damage of important data stored in the system.

Always it is important to keep credentials for important data or system to avoid unauthorized access. So in the recovery phase, the System administrator would login with the credentials and check for possibility of recovering maximum data out of the system.