I usually like to go to YouTube.com and follow JackFrags for these questions. He usually has a really easy step-by-step on how to unlock the videos.
I found this one for you:
Based off of several special pictographs that were found in Dragon's Teeth map pack (eight of which), They placed these in a 64 hexagram table that gives each picture a set of numbers. These numbers correspond with the Fibonacci sequence. Changing them from numbers to tri-pictographs then to unicode decimals, you get a sent of numbers (lots of numbers I won't get into). Getting those numbers, you have to changed them from Largest to smallest.
So you get these long Unicode Decimals, DICE dropped a hit stating that "X marks the spot. The Greek one". Well inside the Battlelog Password screen, the Greek X (CHI) was given a number (7.something).
Well, you Multiple the Unicode Decimal (which we'll call U) and multiple CHI^i++:
Ux^0 + Ux^1 + ... U*x^7
Which equals 24344241893.stuff
In the Password screen, they have a parameter called (max, floor). We used max earlier to change the numbers to start largest to smallest. Now we use the floor method to drop all the numbers after the decimal point.
So, Long story short, the answer is 24344241893. Enter that into Battlelog and you'll unlock the next phantom mission.
Also, from Battlelog itself, a forum dedicated to getting Phase 4.
Granted this is from November 11th. But this should still apply.
How to access the Phantom Terminal
1)Make sure you have premium on your account
2)Go to the LEADERBOARDS page
3)Scroll to the bottom of the page
4)Click the little skull icon to show the Phantom Terminal
Previous Phantom Program Passwords
Phase 1: bumpinthenight
Phase 2: epic dream worlds
Phase 3: 24344241893
Battlefield 4 is known for its in-depth assignments and massive Easter egg hunts. While players were quick to unlock the Phantom Prospect assignment several months ago, the Phantom Trainee has proved more difficult until recently. Thanks to the hard work of several people on Reddit, we now know the password to unlock the Phantom Trainee assignment, with the reward of the Phantom camouflage upon its completion.
Before You Begin
In order to unlock the Phantom Trainee, you must first complete the Phantom Prospect. Don't worry, if you haven't already done so, check out the article we linked above and you'll be done in a few short minutes.
After logging into Battlelog, find your Battlefield 4 profile. Click on the Leaderboards tab at the top and wait for the page to load. Scroll to the bottom of the Leaderboards page, looking on the left hand side for a small skull. Click on that skull to load a page filled with code.
When all of the code has loaded, enter epic dream worlds as the password and press the Enter key on your keyboard. Once you receive a message that it was successful, close the page full of code at the top right of the screen. Don't close the entire webpage itself, just the code.
Head over to the Assignments tab of your Battlelog profile. Scroll down to the Gold Assignments and you will see that the Phantom Trainee is now unlocked. The next time you load up Battlefield 4, there will be a message letting you know that the second phase of the program has begun.
That's all there is to it, except for the 200 kills with pistols, 20 kills in a jet and two shotgun ribbons in a single round. Well, what are you waiting for? Go unlock that Phantom camouflage.