The prince, formally known as the duke of Edinburgh, was responding to treatment for a bladder infection, CNN reported, citing a Buckingham Palace statement. Doctors ordered him to rest, so he was keeping in touch only by telephone.
Philip was taken Wednesday from Balmoral Castle, the royal retreat in the Scottish Highlands, to Aberdeen Royal Infirmary. An RAF helicopter attempted to land at Balmoral but was thwarted by bad weather and the prince instead made the trip by ambulance, The Guardian said.
He is suffering from a recurrence of a bladder infection he developed in June during the celebration of his wife's 60th anniversary on the throne. Philip was also hospitalized at Christmas with a heart problem.
While he announced when he turned 90 that he was giving up some of his responsibilities, Philip, 91, continues to maintain a public schedule -- with and without his wife. His recent activities have ranged from watching the Olympic racing at Weymouth -- he is admiral of the Royal Yacht Squadron -- and being in the stands when his granddaughter, Zara Phillips, won a silver medal in equestrian eventing to attending a Chamber of Commerce lunch on the Isle of Wight.