Both the A and B samples tested positive for the anti-inflammatory substance, salicylic acid, at a level above the permitted threshold. Phillipps could therefore face disqualification from the World Games when the judicial committee of the International Equestrian Federation hears the case next month.
Such a ruling would mean the forfeiture of team bronze medals and the much prized qualification for next year's Olympic Games in Sydney. Three more qualifying places will be on offer at the European Championships in Germany in September, but the British are desperately hoping to keep the place that they won in Rome.
Coral Cove's diet is under scrutiny to pinpoint the potential source of the substance.