His patent was sealed on the 16th of January, 1631.

In the same year the King visited Woolwich to witness the launching of the Vanguard, which Pett had built; and his Majesty honoured the shipwright by participating in a banquet at his lodgings.
From this period to the year 1637, Pett records nothing of particular importance in his autobiography.

He was chiefly occupied in aiding his son Peter--who was rapidly increasing his fame as a shipwright--in repairing and building first-class ships of war.

As Pett had, on an early occasion in his life, prepared a miniature ship for Prince Henry, eldest son of James I., he now proceeded to prepare a similar model for the Prince of Wales, the King's eldest son, afterwards Charles II.
This model was presented to the Prince at St.James's, "who entertained it with great joy, being purposely made to disport himself withal." On the next visit of his Majesty to Woolwich, he inspected the progress made with the Leopard, a sloop-of-war built by Peter Pett.

While in the hold of the vessel, the King called Phineas to one side, and told him of his resolution to have a great new ship built, and that Phineas must be the builder.