Cartyx39,478 Locked 20 Jan 2014 18 Mar 2023
First you need to complete one of the level 20 Main Scenario quests in order to join a Grand Company.
Then once you reach level 50, a quest titled "A Pup No Longer" at your Grand Company will be available. Finish that quest and PvP will be unlocked.
You just need to be in one match to obtain the trophy.
EDIT: Changed level required from 30 to 50.