He founded an architectural firm, Howells & Stokes, with a partner, John Mead Howells, in 1897.
 Their first commission was the University Settlement Society building at 184 Eldridge Street, New York.
 Howells and Stokes were active in New York, but also opened an office on the West Coast in Seattle, designing many of the Metropolitan Tract buildings during the 1910s.
 The partners parted company on amicably terms in the mid 1910s.
 Their work had included the Baltimore Stock Exchange; University site development, Seattle; American Geographical Society Building, New York and the Turks Head Building, Providence.
 Howells continue to design skyscrapers, including the Tribune Tower and Daily News Building, New York, in collaboration with Raymond Hood.

Stokes was appointed by his aunts, Caroline and Olivia Stokes, to design several of their charitable building projects.
 These included: the Tuskegee tenement building in New York (1901); St. Paul's Chapel at Columbia University (1907); Berea College Chapel (1906); Woodbridge Hall at Yale (part of the Hewitt Quadrangle) (1901);  two tenements called the Dudley complex at 339-349 East 32nd Street, New York (1910); an outdoor pulpit for St. John the Divine Cathedral (1916) and memorial gates at both Harvard and Yale universities, Hartford First Church Cemetery and Redlands Hillside Memorial Park Cemetery in California.
 Howells and Stokes also provided designs for the Protestant College in Beirut, an institute supported by the Stokes and Dodge families.
 Caroline Stokes funded work at the Booker T. Washington Tuskegee institutes.
 The architect for these works was Robert Robinson Taylor, who was offered some professional advice by I. N. Phelps Stokes, but this proved to be unhelpful to Taylor who was working with limited resources.

Stokes was involved with family owned property management companies, building and running apartment and office blocks in New York.
In addition to his commercial work, he designed private housing such as Sanger Hill, a New York State country house for his cousin Colonel William Sanger; Beacon Hill House, Newport, Rhode Island for his uncle Arthur Curtiss James; Brick House, Collender's Point, Darien, Connecticut for his parents; and a house for his wife at Indian Harbor, Greenwich, Connecticut.

In 1910, Stokes dismantled a large timber framed house, formerly the Queens Head, located next to what is now the A140 Ipswich to Norwich route in Thwaite, Suffolk, UK.
He transported it in 688 crates from Tilbury Docks to the USA, where it was re-constructed using the timbers of a wrecked English ship, on a hill overlooking Long Island Sound near Greenwich, Connecticut.
It was renamed High Low House (one of its former names whilst standing in Thwaite).
He founded an architectural firm, Howells & Stokes, with a partner, John Mead Howells, in 1897.  Their first commission was the University Settlement Society building at 184 Eldridge Street, New York.  Howells and Stokes were active in New York, but also opened an office on the West Coast in Seattle, designing many of the Metropolitan Tract buildings during the 1910s.  The partners parted company on amicably terms in the mid 1910s.  Their work had included the Baltimore Stock Exchange; University site development, Seattle; American Geographical Society Building, New York and the Turks Head Building, Providence.  Howells continue to design skyscrapers, including the Tribune Tower and Daily News Building, New York, in collaboration with Raymond Hood.
Stokes was appointed by his aunts, Caroline and Olivia Stokes, to design several of their charitable building projects.  These included: the Tuskegee tenement building in New York (1901); St. Paul's Chapel at Columbia University (1907); Berea College Chapel (1906); Woodbridge Hall at Yale (part of the Hewitt Quadrangle) (1901);  two tenements called the Dudley complex at 339-349 East 32nd Street, New York (1910); an outdoor pulpit for St. John the Divine Cathedral (1916) and memorial gates at both Harvard and Yale universities, Hartford First Church Cemetery and Redlands Hillside Memorial Park Cemetery in California.  Howells and Stokes also provided designs for the Protestant College in Beirut, an institute supported by the Stokes and Dodge families.  Caroline Stokes funded work at the Booker T. Washington Tuskegee institutes.  The architect for these works was Robert Robinson Taylor, who was offered some professional advice by I. N. Phelps Stokes, but this proved to be unhelpful to Taylor who was working with limited resources.
Stokes was involved with family owned property management companies, building and running apartment and office blocks in New York. In addition to his commercial work, he designed private housing such as Sanger Hill, a New York State country house for his cousin Colonel William Sanger; Beacon Hill House, Newport, Rhode Island for his uncle Arthur Curtiss James; Brick House, Collender's Point, Darien, Connecticut for his parents; and a house for his wife at Indian Harbor, Greenwich, Connecticut.
In 1910, Stokes dismantled a large timber framed house, formerly the Queens Head, located next to what is now the A140 Ipswich to Norwich route in Thwaite, Suffolk, UK. He transported it in 688 crates from Tilbury Docks to the USA, where it was re-constructed using the timbers of a wrecked English ship, on a hill overlooking Long Island Sound near Greenwich, Connecticut. It was renamed High Low House (one of its former names whilst standing in Thwaite).
Isaac Newton Phelps Stokes