fly the flag

verb2

1. •
   To be registered in a particular country and display that country's flag as a result. (of a ship, airline etc)
2. •
   To support one's country enthusiastically.

   • Now they are the English champions, flying the flag for their country in Europe’s premier club competition and managed by a 53‑year‑old who only got the job on Sunday night. — 2017