Final answer:
Designers Duncan Phyfe and Sheraton contributed to the neoclassic style, known for superior proportions, symmetry, and elegance in line with classical principles.
Step-by-step explanation:
The designers who contributed to the neoclassic style are Duncan Phyfe and Sheraton. Duncan Phyfe was a notable furniture designer whose works are characterized by superior proportions, symmetry, and balance, exemplifying the neoclassical aesthetic in America.
Sheraton, also known as Thomas Sheraton, was an English furniture designer whose published designs in 'The Cabinet Maker and Upholsterer's Drawing-Book' greatly influenced the neoclassical style with their elegance and adherence to classical principles.