This trophy seems to be temprament.
You need to destroy ships inside the Nebula outside of Kijimi, now, rhe way I eventually got this to unlock, after counting 10 whilst I was inside the Nebula and they didn't seem to count, was to lure ships inside with me.
They and your ship should both be in the Nebula to be safe, make sure they are Pirate ships and you don't accidentally fire on Empire ships in the area.
What the games counts as the Nebula is also contentious. It's best to bring the ship into the the dust clouds and track them using R3 to make sure they are still inside the dust when you shoot them down. The Nebula should disable your rockets, but my final destroyed ship, my rockets where active at the bottom of my screen, so after some resesrch I discovered this trophy seems to track differently user to user or it has quirks to it. Which is why I say make sure your Rockets are disabled before finishing destorying a ship and that the ship itself is in the Nebula dust using R3.