Predecessor Builds > Phase > Phase Be Nimble, Phase Be Quick

Doubling up the greaves makes for some fun. Mana regen and ability haste keeps you in the thick with the team longer.

Early game:
Focus on hit and run tactics to draw minions to your carry and trade auto dmg with the enemy carry. Try to make them focus on you as much as possible to give your carry the edge in farm (this is what Phase's kit is good at, being the distraction). Careful, this is where you will end up dying the most if you poke through minions in the first couple waves. Once Galaxy Greaves is up, you should have a more comfortable time harassing the enemy duo. Once Marshal is up, you should be able to start pushing to take tower and not have to worry about mana levels pretty much ever. Your starting play appears aggressive and your carry might mistake this for a push when its not. The goal is to pressure enough to be the target but not full-on push at the beginning.

Midgame:
Gaia Greaves will improve durability and also help with mobility in rotations (Phase base movement is 645; Galaxy adds 64.5 and Gaia adds another 60 for a total movement spd of 769.5 out of combat (I have been informed that it may be higher if the galaxy calculates gaia bonus spd into its 10%). Assassins like Kallari and Countess have a base 680 for context.). You should be relying on your link/passive to keep your carry alive, so spam those abilities! If you have a carry that can take advantage, your armor boost should allow you to initiate fights with flare and then use galaxy jump to escape. The key to this build is the hit and run. Even if you get cc'd there is a good chance at escape. With two armor items you can actually be able to initiate team fights at objectives; galaxy jump into the middle of the enemy team and use your flare and then take advantage of Gaia's 75% jump boost to use your Lance as an escape (be the flashbang for your entry team).

Endgame: You can go several different ways after Gaia... If they are particularly magic weak go the ability damage route. You could augment the physical damage of your carry with the on-hit damage build. Most of the time you'll be trying to spread the anti-heal and keep your team topped off though so the default build focuses on that. With the default, void conduit is kind of nice but it might be better to have lunaria instead. Spellshield is a nice way to top off the build and make you super frustrating to deal with but Astral catalyst is more useful on Phase as takedowns you assist in will decrease cd on your ult.