Beaver was born in Lewknor, in Oxfordshire on 28 February 1766 to the Reverend James Beaver, curate of Lewknor. His father died when Philip was eleven, leaving the family impoverished. His mother accepted the offer of Joshua Rowley, then captain of HMS "Monarch" to take Philip to sea with him. Philip Beaver entered the Navy in October 1777, becoming midshipman aboard the "Monarch" during 1778. Whilst in this post, he witnessed the Battle of Ushant on 27 July 1778. He remained with Rowley and accompanied him when Rowley took command of HMS "Suffolk" in December 1778 and sailed her to the West Indies. Rowley was then appointed rear-admiral and hoisted his flag in a number of ships, including HMS "Conqueror", HMS "Terrible" and HMS "Princess Royal". Beaver followed him to each one, and in doing so served as part of fleets between 1779 and 1780 at times under the command of Admirals John Byron, Sir Hyde Parker and Sir George Rodney. His ship then came under the overall command of Sir Peter Parker at Jamaica, where Beaver spent the rest of the war. He was promoted to lieutenant by his patron, Admiral Rowley, on 2 June 1783. He spent the next ten years living with his mother at Boulogne. His naval service during this period was limited to a few months in 1790 and in 1791, during the mobilizations in response to the Spanish and the Russian armaments.