Their amazement grew when they returned in daylight to find enormous paw prints in the mud and a strange 'lair-like' structure.
And now an expert has backed up their sighting by examining photographs and declaring the paw prints to be much larger than those of a domestic cat.
Tom Larkham, from Shrewsbury, who was a cat keeper at Chester and Dudley zoos, says the prints are about the size of an exotic, jungle cat.
And he says the animal could be a descendent of a jungle cat that he remembers being found in Shropshire in the 1980s.
Mrs Phillips, a teacher, said: "I was driving from Ellesmere to St Martins when not far from St Martins Lynda shouted: 'What was that?' She had seen eyes gleaming from the hedgerows then suddenly she said the animal just took off and leapt straight over the fence and into the field.
"She was so adamant that the animal was too big to be an ordinary cat, so we returned in daylight. Once we were in the field we actually couldn't believe the size of the paw prints that we found and also the gait of the animal. It must have had a stride of about three feet."
In the corner of the field there was also a strange lair-type structure, made from the stubble in the field. Fascinated by the size of the paw prints, captured on photographs, staff at the Shropshire Wildlife Trust forwarded them on to Mr Larkham.
He is now a teacher at Coleham School in Shrewsbury, but gained a zoology degree and worked as a student zoo keeper at Chester Zoo with the large cats and then had a job with the big cats at Dudley Zoo. He stressed that the animal would not be a big cat like a panther.
"The paw prints are smaller than that but certainly much larger than a domestic cat. It is either a gigantic domestic cat or something the size of an exotic pet such as a jungle cat."
Mr Larkham said people need not worry about the cat being a danger to lambs and other animals.
"The rabbit population may be a bit nervous but animals of this size wouldn't go for lambs."