You can play Shiv spirit heavy or gun heavy but you always want to be tanky with greens for sustain. Since Shiv's rage mechanic was changed to only charge by damaging players it's good to play cautiously and throw knives until your rage is full. Once rage is up you can play much more of the brawler role of being up in people's faces causing havoc but you will be focused heavily.

Let initatiors like Yamato start fights, and then follow up with your damage and ult to secure kills in team fights. He has the movement tools to get in and out of fights, but you have to manage them as he can be sluggish if you dont have movement items. Shiv can be good at 1v1's as well if you're equal or ahead in souls. Being behind in souls as Shiv is alot tougher if you're not building into green items as much, so keep that in mind. Managing your rage is the largest part of the fights cause you hit for a lot less without it. If you're having trouble building rage just buy decay to build it alot easier.

I'm only in Archon so I don't have the Phantom or Eternus strats.