Although he held such a junior rank, Philip’s numerous social and political connections led to his appointment in December 1915 as private secretary and general fixer for Field Marshal Haig, who was Commander in Chief of the British forces in France and Flanders. Today, we might recognise his role as a special adviser. His duties included liaison with allies, organising Haig's diary and correspondence with newspaper proprietors, particularly Lord Northcliffe who was critical of the conduct of the war and used The Times and Daily Mail to set out his opinions.
He was a fluent French speaker and was at the meeting on 1st December 1914 at the Chateau Demont at Merville in France, when King George V and Edward Prince of Wales met Poincare, President of France, and Generals Joffre, Foch and Rawlinson. At this meeting the allies showed their determination to fight Germany and the Central Powers.