The Trophy progression bar is displayed at the bottom of the Home Screen and at the top of the Pit Pass screen. This shows how many more Trophies you need to collect until you reach the next Milestone. The number at the end of the bar is the Milestone number you are trying to reach.

Once you have collected the amount of Trophies required to reach the Milestone, the bar will then reset to show how many you then need to reach the next!