Jones will play a nurse in the show, called 'The Ark', alongside stars including Oona Chaplin, Hermione Norris and Kerry Fox.
Phelps, who has written the six-part series, said: "I am bouncing off the walls with excitement at having such an extraordinary talented cast, bouncing off the walls."
Jones said: "This is my first period drama and I am so excited at the prospect of filming a First World War series set on a frontline hospital.
"It's an important period in history not just because of the war but because it was a transitional period for women, liberated in some respect but still shackled by the conventions and hierarchies of the past.
"Sarah Phelps really gets to the beating heart of a story and gives very strong images and weight to her characters.
"For my role as Joan she has created a nurse with a very independent and modern outlook who is much more interested in her patients than protocol.
"I am really looking forward to getting started and it will be great to work once again with director David Evans."
Filming on the BBC One drama starts this month.