The bulk of papers pertain to W. L. Phillips' career, from his work at Harvard University in the early 1900s to his involvement in numerous landscaping projects through the late 1950s, with substantial portions of this data relating to the Mountain Lake Sanctuary and Royal Palm State Park.

Among the records are letters, invoices, notes, clippings, sketches, reports, planting lists, contracts, specifications, photographic prints, negatives, pamphlets, and ephemera. Documents related to professional organizations and awards are also included. A set of alphabetized index cards bears notes concerning landscape architecture, astronomy, investment information, property data, and other topics. In addition, notebooks of Harvard class notes, classified plant lists, and field notes and sketches augment the collection.

Supplementing the papers regarding professional projects are original plans and blueprints, as well as several maps. Where indicated in the files, photocopies of some plans substitute for the originals, which are located at the University of Miami library.

Also maintained in the collection are papers documenting Phillips' personal life spanning the early 1900s to the mid-1960s. Correspondence with family members and friends, school records and notebooks, an address book, birth and death records, passports, identification cards, certificates, travel brochures, clippings, and other ephemera comprise this material. Financial and property records include bank statements, correspondence, mortgage papers, investment documents, and tax information. In addition, the personal data contains a 1992 historic designation report for Phillips' North Miami residence. Two pencil drawings found among the papers depict the figure of an unknown youth and a signed portrait of William Lyman Phillips.