He won a Silver medal with the British team at the 1988 Olympics. Mark was also a four time champion at the Badminton Horse Trials. Through his equestrian activities he met Princess Anne. The two married in 1973 and has two children. They divorced in 1992 and Mark gained a small settlement. Phillips designed a cross country venue for the Red Hills Horse Trials. He serves as a columnist for Horse & Hound magazine and is Chef d’Equipe for the United States Eventing Team.