Pentagon City was founded in 1946, when developers Morris Cafritz and Charles H. Tompkins acquired a 190-acre site of empty fields and commercial warehouses for $1.5 million.[2][3] A Western Electric telephone manufacturing facility opened in the 1950s and was later converted into a small shopping mall known as "Pentagon Centre." In the 1960s, high-rise apartment buildings were erected on Hayes, Fern, and Joyce Streets.
It was not a manufacturing facility. It was a refurbishing plant.
“We processed all the phone equipment that was removed from houses and businesses within the C&P area, which included the District of Columbia, parts of Virginia, Maryland, West Virginia, and Delaware.”
http://cowboyfrank.net/telephones/weco/index.htm
It also had nothing to do with the demand for telephones from the Pentagon.
Additionally, Western Electric did not consider it a manufacturing plant, as it was not on their 1967 list of manufacturing plants: