The 30-year-old was crowned the winner in an event at the Johnson and Perrott Land Rover International Horse Trials at Ballindenisk in Watergrasshill.
Agriculture Minister Simon Coveney was on hand to present her with her prize.
Sitting astride her horse Lord Lauries while the British national anthem was played, Ms Phillips was all smiles.
She then participated in a lap of honour with the other top six scorers before giving the crowd a quick wave.
Ms Phillips, a grand-daughter of Queen Elizabeth, flew into Cork on Thursday as footage emerged of her husband Mike Tindall with his arm around a blonde woman in a bar in New Zealand as the England team celebrated their win over Argentina at the World Cup.
It was later revealed the woman, who was on holiday in Queenstown, was an old friend of the player from his university days.
Ms Phillips is believed to be flying out to New Zealand soon to join her husband at the Rugby World Cup.