MLA

Stein, Gertrude, 1874-1946. Gibb, Henry Phelan. Box 108, folder 2155-2156. 1911-33, n.d.. https://collections.library.yale.edu/catalog/17105738.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 108, folder 2155-2156"])(1911-33, n.d.)[Gibb, Henry Phelan]. https://collections.library.yale.edu/catalog/17105738.