These three bad boys allow Phantom Lancer to become a tanky, dangerous and inescapable foe, impossible to defeat 1v1.
The Diffusal Blade will be our first pick-up, because of its great value. It has two amazing effects; mana burn and purge. The mana burn deals 20 flat damage and removes 20 mana from your enemies on each hit. The best part though? Your illusions ALSO get the +20 mana burn. For 8 illusions+PL hitting at the same time, that basically means +180
extra damage. And that's on a level 1 diffusal, level 2 gives you +36 per hit...
Purge is the second, and active ability the Diffusal has. Purge allows you to slow one enemy target for 4 seconds as well as removing any buffs, making this a great item for chasing enemy heroes. But that's not the only thing Purge can do. It deals 99999 damage to summoned units- instantly killing them. Say goodbye to Warlock's golems and Anti-Mage's Manta illusions.
You can also use Purge on allies and on yourself, allowing you to get rid of revealing effects like Bounty Hunter's Track and Dust.
Most players upgrade their Diffusal once they run out of Purge charges, because it refills them, but depending on whatever situation you find yourself in (if you're lacking damage and don't have a lot of money, for instance) you could upgrade it earlier.
A Manta Style is your second big pick-up. The Yasha gives you extra attack and movement speed, which, coupled with your Drum and Diffusal, makes you impossible to chase or run away from. Its active allows you to spawn 2 illusions. Keep in mind that Illusions spawned from a Manta or Illusion Rune don't affect your 8 Juxtapose illusions, so you'll be able to get up to 10 now!
A great way to gank people is to use Doppelwalk to become invisible, run up to your enemy, use your Diffusal and Manta and kill them before they even realise what's happening. It's also great for pushing lanes while you're in the jungle.
A Heart of Tarrasque finishes your core. Not only does it give you and your illusions roughly 1000 more HP, it also gives the main PL incredible HP regeneration, allowing him to jump back into battle at a moment's notice.
Do note that the order in which you get these items is not strictly rigid. If you feel you need more tankiness ASAP, then feel free to rush that Heart! I've found myself sometimes getting Manta before Diffusal when I felt splitpushing and getting a few extra stats were the best idea.
Choosing lategame items for Phantom Lancer can get a bit confusing, because there's barely any really expensive items that help your illusions. A guaranteed pickup, however, is the Butterfly.
You thought that Heart made your illusions hard to kill? Wait till you get a load of this! Not only does it give your illusions +30 AGI and +30 attack speed, it also gives them a 35% chance to avoid physical attacks
Ditch those Power Treads and get Boots of Travel to splitpush everywhere
Get a bunch of illusions in one lane (you may choose to use your Manta here) and teleport your hero to another lane and push that out too. Double the money! C9.EternalEnvy once used a strategy where he rushed brown Boots, Drum, Manta and Boots of Travel, without even getting a Diffusal Blade. This allowed him to splitpush down towers very easily, while his team kept the enemy distracted.
Now, Illusions don't benefit from flat damage increase, but they do get some buffs. The Daedalus allows your illusions to crit for 2.4x their normal damage on 25% of their attacks. Do remember that the big number that appears above their heads isn't the actual damage dealt- it's only 25% of that number.
If you're up against nasty evasion-centric heroes like Brewmaster, Phantom Assassin or anyone else who might pick up a butterfly, a Monkey King Bar could help. Your illusions don't get the extra damage or bash, but they do benefit from True Strike, making their attacks undodgeable. When you find yourself unable to kill a PA even with Diff/Manta/Heart, it might be a good idea to pick this up before your Butterfly.
An Abyssal Blade allows you to lock down annoying slippery enemies like QoP and Anti-Mage, as well as fed heroes who clear away your illusions before you get a nice surround like Sven, Medusa and Gyrocopter.
If you really think you're still not tanky enough (which, honestly, is hard to believe), the armor aura of an Assault Cuirass should do the trick. Alternatively, you could get a second Heart.