Born in Boston in 1923, Lawrence Irving Phelps demonstrated remarkable musical ability from an early age. He learned to play the piano at age six and could play most band and orchestral instruments by the time he graduated from high school. He built his first organ at the age of 17, using old parts and what knowledge he could glean from books.
At the New England Conservatory in Boston, where he studied music history and theory in the early 1940s, Phelps was in charge of maintaining the school's 15 organs. In 1944 he became an apprentice to organ reformer G. Donald Harrison at the Aeolian-Skinner Organ Company.
Harrison and Holtkamp represented growing dissatisfaction with the muddy tones characterizing organs of the early 20th century. Their innovations resulted in brighter voicing and less apparent orchestral imitativeness. While the increased sound quality was an improvement, Phelps believed these changes failed to recognize the organ as a means of communicating musical ideas. In the words of a Lawrence Phelps and Associates publication: "Lawrence Phelps, trained to think and hear as a musician first and a technician second, remained largely dissatisfied with these essentially superficial improvements and, working always from his knowledge of the organ's centuries-old repertoire, sought to develop the organ to the point where every part of its design reflected the fulfillment of a musical need."