Make sure you have the Premium Edition of Battlefield 4, and play at least one match online as a Premium user. If you have the game on Steam, it should be the Premium Edition by default, so don't worry about making any extra purchases.

Access and log into Battlelog:
https://battlelog.battlefield.com/bf4

The secret skull from the Battlelog website has been moved. Old guides say it's in the leaderboards page, which is no longer the case. It is now located in the age ratings page.

Log into battlelog, scroll down, and click the "Age ratings" link on the bottom of the page:

Alternatively, you can just click this link: https://battlelog.battlefield.com/bf4/agerating/

After that, scroll down once again, and click this skull icon:

Once you have clicked the skull, you'll be greeted with a screen similar to this one:


My screen looks a bit different, and mentions "Phase 4 is now active." That is because I have already entered the codes and activated the assignments. If you haven't yet done that, you must enter the following codes in order, without the quotation marks, to unlock each of the three assignments:

• “bumpinthenight” - Phantom Prospect
  
• “epic dream worlds” - Phantom Trainee
  
• “24344241893” - Phantom Initiate

Press enter in between each of the codes.

You can track them in-game or in the Battlelog website itself.

Phantom Program Dog Tag




Phantom Paint




Phantom Camouflage

After completing all three assignments, you can unlock the Phantom Operative assignment through a long and complicated easter egg that I won't cover in this guide. If you want to know how to do it, click this link to the Battlefield wiki and follow the instructions for the old method of unlocking the Phantom bow in Hangar 21: https://battlefield.fandom.com/wiki/Phantom#Unlocking

Note that this method is no longer needed to unlock the Phantom Bow itself, as there is now a much easier way to do it by finding it in the map Operation Outbreak. You can check out the details for that method in this simple guide:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2737250740

If you want to complete Phantom Operative anyway, you can find other players with the same goal in the comments of this guide. You are going to need three other players to do it.

You can help increase this guide's visibility by rating it. If you want to give the guide's creator some Steam points, leave an award.

If you have noticed a mistake, feel free to leave a correction in the comments.