Phebe Robinson Jacobsen was born in Baltimore, In 1922 and graduated from high school in Westminster. In 1943, she married Bryce Jacobsen. After attending Western Maryland College where she earned a bachelors degree in History and English, and teaching high school, Jacobsen began her archival career.
Jacobsen worked for Historic Annapolis and the Pennsylvania State Archives before aiding author Alex Haley in discovering his ancestors, leading to his Pulitzer Prize-winning book Roots and the television miniseries Roots: The Saga of an American Family. Leonard Blackshear, chairman of the Kunta Kinte-Alex Haley Memorial Foundation of Annapolis and longtime friend of Jacobsen described her as the unsung hero of the Roots saga.
After her retirement in 1990, Jacobsen continued to conduct genealogical studies and research into Marylands Native Americans from her home near the Navy-Marine Corps Memorial Stadium. Her husband passed in the spring of 1998. Soon after, Jacobsen died at the age of 78 from complications of diabetes at her Annapolis home.