Along with his father, William Henry Phelps, he founded the first commercial radio station in Venezuela, 1 Broadcasting Caracas.

After finishing his studies at Lawrenceville School and getting a BSc in 1926 from Princeton University, he published over 78 books on the birds of Venezuela with his wife Katherine Deery Phelps, in which they described their discovery of more than 200 new species.

A direct result of his research was the creation of the Venezuelan Museum of Ornithology with one of the most important libraries and collections in South America.

In recognition of his research the University of Exeter created a fellowship in his honor to fund Venezuelan graduate students interested in zoology.

In 1953 he founded one of the most important Venezuelan television stations, Radio Caracas Televisión, and served as its president for 34 years.