I found this trophy frustrating as a returning player looking to clean up trophies, given changes and updates to the game since release. Here is what I did:
1. Started a new character at level 1. Played through the introductory missions until I reached The Farm (less than 1 hour).
2. Spoke to Shaxx. Opened the Director and pressed L2 to see "Play two Quickplay Crucible matches". No matter win or lose.
3. Updated to "Play two Competitive Crucible matches".
4. Return to Shaxx and turned it in. Trophy unlocked.
Nowhere does it say "Call to Arms".