Phelps was also a landscape designer, who was hired by Henry Fownes Luttrell to update the grounds of Dunster Castle.
[1][2]: 349 He had land holdings in Porlock, not far from his friend Coplestone Warre Bampfylde's estate, Hestercombe House.
The works include portraits of gentry, self-portraits, landscapes, genre paintings, religious studies, and grotesque figures.
Some of the drawings are made after the works of other artists, like Rembrandt, Thomas Hudson, Joseph van Haecken.
[8] Phelps was hired by Henry Fownes Luttrell to design Conygar Tower, landscaping, and bridges for Dunster Castle.
[9][10] Conygar Tower is a three-storey folly built in 1775 on the top of a wooded hill overlooking the village of Dunster.
It was made of local stone, brick capping, and pebbles and designed with a rustic, picturesque style.