Phillips was signed up as a brand ambassador for Musto earlier this year and has previously appeared in its advertising.
The range includes jackets and fleeces, and will be launched to the trade in early 2010 and will go on sale in August.
All products in the clothing range will carry Phillips’ eventing number “176” as a logo.
Phillips is the daughter of the Princess Royal and her first husband, Captain Mark Phillips. She is an equestrian and was voted BBC Sports Personality of the Year in 2006.
Musto is better known as a sailing wear brand but in recent years has expanded its reach into lifestyle outdoor clothing including shooting and equestrian.