The 2006 world eventing champion missed out on both the 2004 and 2008 Games after her horse, Toytown, sustained injuries that shattered her own Olympic dreams.
Phillips, whose mother Princess Anne competed at the 1976 Olympics and father Mark Phillips won gold in the 1972 team event, will join William Fox-Pitt, Mary King, Tina Cook and Nicola Wilson in a strong British quintet that is action on the full first day of the Games in Greenwich.
"My horse High Kingdom is very different from Toytown," she said.
"It's now about preparing to get the peak level of performance, although you obviously want to stop anything from happening.
"But animals do stupid things, it's part of the sport unfortunately.
"However, he's getting better and better in dressage because that's where he is weakest.
"Hopefully, he's going to improve again in the next couple of weeks."
Fox-Pitt, part of the squad that won bronze in Beijing and silver in Athens, believes the roster of riders is strong enough to challenge the best in the world, including defending champions Germany, and land their first Olympic team gold in 40 years.
"Gold is out there for us, it won't be easy but it's not out of reach by any means," he said.
"It's a good team, an exciting team. Hopefully things go our way and we've got a good chance."