I don't think he fits the team's style any more. There was a noticeable improvement in our solidity and balance after he left; most people would never think 32 year old Milner playing in his place would make us better, but on balance he did. We lacked in creativity sometimes, but the control was much, much better – no more see-saw games like the 2 CL draws against Sevilla or painful collapses like the EL final, again vs Sevilla (where Coutinho was completely missing in the 2nd half – something that's hard to imagine any of Klopp's players doing in a big game now). This extra solidity elsewhere allowed Salah in particular to have the freedom he needed to play the kind of superhuman season that he did, which more than compensated for any goals Phil could have scored.
Looking at Coutinho objectively, as just another player we could sign, I would say he definitely doesn't fit the requirements for a midfielder on this team. He could play on the wing in place of Mane – but even then his lack of speed and tracking back would create a certain imbalance, especially since Salah on the opposite flank is usually freed from defensive responsibility. We would then have a similar problem to Arsenal with Ozil and Aubameyang providing no protection down both wings, which makes their defense always somewhat vulnerable.
Coutinho is better than Shaqiri, but ultimately I could see him fitting in only in something like a "Shaqiri role" – an additional creative spark off the bench or for specific (rare) games where Klopp is willing to sacrifice defensive balance. Obviously he would be way, way too expensive for that.
