MLA

Bryher, 1894-1983. Frere, Philip. Box 108, folder 3874. n.d.. https://collections.library.yale.edu/catalog/17290881.

APA, 6th edition

Bryher, 1894-1983. (["Box 108, folder 3874"])(n.d.)[Frere, Philip]. https://collections.library.yale.edu/catalog/17290881.