Depending on how closely you've been following information coming out about The Division, you may or may not have heard of Phoenix Credits already. You might have just finished the story mode, reached level 30, and only just found out they exist. Or maybe you're lower level but have heard whispers about what's to come. Whatever the case, this guide breaks down the entire system for you.
Alright, so you've hit level 30 in The Division, and you realise that's the cap. You can level no further. Well, there are still ways to improve your agent, because their stats are determined by their gear, not their level. You can probably see where this is going. Phoenix Credits are the hard to earn currency you can use to buy high–end weapons and gear to continue your quest to be the bad–assest agent you can be.
Phoenix Credits are hard won, but there a few ways you can do it, though it's important to note that these only become available once you hit level 30, so there are no shortcuts or farming for them before the endgame. You'll also earn Phoenix Credits from Incursions, once they're added as part of the DLC.
In the normal game missions have two difficulty levels: normal, and hard. The endgame unlocks the ability to play story missions at challenging difficulty. 'Challenging' is a pretty coy way of putting it, though, when a more accurate title would be 'That's It, Man. Game Over, Man. Game Over!' Mode. Almost every enemy you'll face will be an elite, and can even one shot kill you if you've not geared for stamina enough. Completing a mission at challenging difficulty gives you 30 Phoenix Credits.
After you've hit level 30 you'll start getting the daily missions. Every day you can complete up to three missions selected as the daily ones (they'll have a white circle around their icon on the map). Completing a daily mission on hard difficulty gives you 15 Phoenix Credits, whilst completing it on challenging gives you 20. You also get rewarded with items and crafting materials.
They're not bosses exactly but at level 30 you'll start getting some named elite enemies appearing in the DZ, including DZ1, who drop various amounts of Phoenix Credits as part of their loot. These enemies will spawn in the same areas of the map, but are randomly drawn from a pool of several different ones, so you'll never know who it is you might be facing (which makes it harder to plan tactics ahead, and is all part of the rich, exciting challenge).
Currently there are only two vendors that accept Phoenix Credits as currency: the dude at the top of the stairs in the Tech Wing of your Base of Operations, and a Dark Zone vendor in a safe room in a church, in the top corner of DZ6 (and this vendor will only accept Phoenix Credits). High–end items are so rare that buying them in the endgame is basically the only way you'll get them.
These vendors also carry really good weapons and gear of other quality, of course, and the DZ vendor also sells cosmetic clothes items for Phoenix Credits. But you'd be mad to spend them on clothes. Because they do nothing.