Badminton Horse Trials
Date: Thu 1 May-Sun 4 May Venue: Badminton, Gloucestershire
Coverage: Full coverage on BBC interactive and BBC Sport website (UK only) from 1100-1700 BST on Saturday. BBC2 1300 BST-1500 BST on Sunday
Phillips had a poor dressage display on her second ride
Australia's triple three-day eventing Olympic gold medallist Andrew Hoy moved into the lead after two days of dressage at the Badminton Horse Trials.
Hoy and Moon Fleet, who are seeking qualification for this year's Olympic Games, hold a 0.7 penalty lead over Briton Ruth Edge and Muschamp Impala.
But it was not such a good day for world champion Zara Phillips, who slid back to 18th place on Glenbuck.
Her second mount, Ardfield Magic Star, was even further back in 76th.
"Ardfield Magic Star got very tense," said Phillips. "It all depends what mood he is in.
"If he decides not to be co-operative, I just have to go with it and not ask him questions."
Devon rider Lucy Wiegersma lies third on Shaabrak while veteran Pippa Funnell is equal seventh and William Fox-Pitt equal 11th on Tamarill.
Britain's Olympic Games hopefuls are competing to impress selectors, who will aim to finalise the equestrian squad after Badminton.
Hoy, who is looking to qualify as the oldest member of the Australian team at the age of 49, said: "It was a great success.
"But I had to give Moon Fleet a sharp canter just before going into the dressage arena when he coughed and I realised he needed to clear his wind.
"This is only his second start in 12 months but the time off has given me a really good chance to get him at peak fitness."