Courtenay was born on 18 January 1404, the eldest son and heir of Sir John Courtenay (died before 1415) of Powderham, by his wife Joan[3] Champernoun (died 1419),[4] widow of Sir James Chudleigh[5] and daughter of Richard Champernoun of Modbury.

He had been badly treated by his distant cousin Thomas de Courtenay, 5th Earl of Devon (1414–1458), whose seat was at Tiverton Castle, and during the turbulent and lawless era of the Wars of the Roses, he supported the challenge against the earl, for local supremacy in Devon, put up by the Lancastrian courtier, Sir William Bonville (1392–1461), of Shute.

On 3 November 1455 Thomas de Courtenay, 5th Earl of Devon (1414–1458) at the head of a private army of 1,000 men seized control of Exeter and its royal castle, the stewardship of which was sought by Bonville, and laid siege to nearby Powderham for two months.

Lord Bonville attempted to raise the siege and approached from the east, crossing the River Exe, but was unsuccessful and was driven back by the Earl's forces.

[9] Sir Philip swore fealty to King Edward IV (1461–1483) as an MP at Parliament.