This is more a task for you to understand the manual. Not sure how you have done the rest before.
On page C3 of the manual you get a command overview. ESC E is the command to select a bold font (details on page C110). You want to change the font size so you need ESC P, ESC M or ESC g.
ESC stands for the escape character, decimal index 27 in ASCII table or hex 1B or octal 33. Place "\033P"
within your string to try out as that is the way you include a special char with octal code in PHP String manual.