Sir William Phelip was son of Sir John Phelip of Donnington, Suffolk, knight, and is described as being a valiant soldier in the wars in France during the reign of King Henry V of England. He became Treasurer of the King's Household, and on the King's decease had the chief conduct of his funeral. He is said to have been created Lord Bardolf by Letters Patent of Henry VI but it does not appear that he ever had a summons to parliament, although he bore that title. He was a Knight of the Garter, and Chamberlain to King Henry VI.
Sir William Phelip married Joan daughter and co-heir of the attainted Thomas Bardolf, 5th Lord Bardolf and it was by this route that he acquired his peerage. Lord Bardolf's estates had been divided between Thomas Beaufort, 1st Duke of Exeter, the king's half-brother, Sir George Dunbar, knt., and the Queen, but the latter's proportion, upon the petition of Sir William de Clifford, Knt., and his wife Anne (née Bardolf) and Sir William Phelip and his wife Joan (née) Bardolf), to the King, was granted in reversion, after the Queen's decease, to those representatives of the attainted nobleman.
His wife died before 1447, as in that year the Executors of Joan, Lady Bardolf, sold her property of Erpingham manor, in St.Martin's at the Palace, at Norwich, to William Calthorpe.