Phantom Assassin is a agility hero which makes her good for escaping but also good for carry and ganking.
Phantom Assassin can kill enemies in an instant
+One of the highest potential lategame DPS
+Decent farming ability
+Can kill enemies quick
+Good for escaping
In the early game you can somehow harass you're enemy heroes by using Stifling Dagger on them. When you have the Phase Boots you will be able to battle one of you're enemy in you're lane, you're Poor Man's Shield will give you additional blocks which will help you on fighting enemy heroes or creeps. If you have enough money or a 1,200 gold, I recommend you buy the Morbid Mask first so that you can start you're farming.
In the mid game you will be able to kill or hunt enemies better because of the help of you're Vlad and Phase Boots. If you already bought the Battle Furry you should be able to farm faster now and take on ancient creeps in the jungle easier, which will help you to earn golds faster. In this time of the game you should be able to kill enemies allot easier now because of you're Desolator and Skull Basher which lowers you're enemies armor and stun them for a while and they will be vulnerable to attack and kill.
In the late game you will have more advantage on ganking enemies because of you're items like the Abyssal Blade which have a passive and avtive stun which allows you to stun them twice leaving them no choice but to run until they die. And you're Bkb will help you when going into a clash. In the late game if you're SS is triggered you're critical strike will be 1k which makes you're enemy's HP to be very low.
First I use my 1st skill then second skill and if my target tries to escape or run i use my Phase Boots to chase my target and while running i wait for my skills to recharge and if they are recharged i use them again. But sometimes instead of waiting my skills to recharge while chasing my enemy i use my Abyssal Blade on my target then 1st and 2nd skill for a sure death. When going into a clash I activate my Black King Bar (Bkb) first for additional spell immunity (something like that) and I use my skills and my Abyssal Blade and Phase Boots to chase my enemies or for escaping when I have low health.
Hey guys thanks for taking a peep on my guide. Hope I helped.