The 39-year-old from Neath competed at Athens 2004 and Beijing 2008.
The cause of death has not been confirmed.
"All at UK Athletics send our deepest sympathies to the family and friends of Philippa at this sad time," UK Athletics chief executive Niels de Vos said.
Her best throw of 62.89 metres, achieved in 2003, places her fourth the British all-time rankings.
Wales' 2008 discus champion also placed fourth at two Commonwealth Games, in Manchester and Delhi, and sixth in Kuala Lumpur and Melbourne.
Welsh Athletics Head of Coaching and Performance Scott Simpson said: "We are all shocked and deeply saddened by this tragic news.  We are currently awaiting more information surrounding what has happened.
"Philippa was one of Wales' finest ever throwers, excelling across all disciplines, but particularly in the discus.
"Her bubbly personality always brought a smile to those around her and she will be remembered as the life and soul of the Welsh teams that she was a part of.
"Not only the best teammate that one could have wished for, she was an inspiration to many and a great role model for future generations of athlete across all disciplines.
"She will be sorely missed by all that knew her and we would like to send our deepest condolences to her family and friends during this most difficult of times."
Welsh discus thrower Philippa Roles, who represented Great Britain at two Olympic Games, has died, UK Athletics has announced.