Also consider a frostburn instead of myth/aftershock.

Phinns got a good threat meter. For example another Phinn, DEFINITELY Skaarf with that large burn damage taking off max health, and skaarf just regens it all since you so tanky, ringo hellfire brew on CP ringo may not outright remove you from a fight but it still HURTS, and Saw can chow down on you if CP assassin with Aftershock Roadie Run followed by Mad Cannon, Catherine can silence you to make sure her team escapes, and stormgaurd your quibble to reflect damage back towards your team, especially if you are CP phinn (Which is OP as a warrior), and her merciless pursuit won't stun you but it still gives a Captain of the Guard stack, but you are too slow to punish her for it. Riem's passive perk plus Winter Spire and your slow speed can do a lot more than you think if he builds Frostburn, Broken Myth, and goes for Journ Boots early game.

Also, think Phinn would be broken if he could use his ult to pull back his teammates too (Like out of Ardans Ult Arena and stuff). Course itd invite trollers to get 6 clockworks on phinn and do nothing but pull back your teammates every moment you can, but it'd become a very versatile and useful Ult. Well more so than it already is (I hate when phinns use their ult in conjunction with turrets. Ult, Quibble, Polite Company, they die.)

Just my thoughts on the matter. And thanks for making sure petal was not placed in the Potato Throne. She aint no potato anymore.

I have just tried Phinn recently as I have a hubch that he will be the next op within the few patches.

You build is greate, but I would like to make a suggestion that if your enemy team consist of fragile laner and jungler, shatter glass is a better first item to rush as I found the A damage is enough to one-shot any squishy heroes when their hp is something below 70%.

In addition, I would also recommend clock work as a fourth or third item because the hook can be used more often which is very crucial in soloque.

im not a huge fan of phinn totally because going against him is a huge headace. But i just used him following this guide, i bet the other team had experienced what i had against him XD. He has so much health and good damage, though in the end we won, he was really slow, he starts getting a little bit more death showing him as a bigger target because to get rid of the trouble from his huge health and his slow mobility (probably the slowest hero in the game) as he acted almost a replica of the Kraken. He acted as a huge barricade/shield for team mates allowing them to make the kills. This guide is totally recommended though could include shiversteel/Crucible/fountain renewal instead of Aegis since metal jacket is included (unless buff up shileds for CP attacks) but other wise this guide highly recommeded.
Good Job :D and MERRYCHRISTMAS! (& a happy new year)
DGo

This is Shin's build...https://www.youtube.com/watch?v=Gi245AleYXI