The corporate you is defined as talking to any employee as though they are the business as a whole. Example of the corporate you: "Excuse me, do you have any more of these in stock?"
It is like the opposite of the royal we. Its when you use the word "you" to an employee, but you arent referring to them personally, you are talking about the business using the employee as a stand in, because the corporate entity is not alive and cannot hear or answer for itself
A 'ladder' is a device with steps used to 'climb' (or move) up and down, so the 'corporate ladder' is the series of steps people go through as they gain more power in a corporation and 'rise to the top' - from file clerk up to president.
This pharse refers to moving up in rank within a particular field or business. If someone "climbs the corporate ladder" to the top, they started out at the bottom (stockboy, mail clerk, etc) and ended up at the top (CEO, CFO, vice pres., etc.)
Tim lived the American Dream. He started out as a desk clerk and climbed the corporate ladder to the top. He is now a CEO in the same field that he had started out in.