So keep him as a third or fourth option. Don't prioritize the guy that is going to win headers against Chris Wood, that shouldn't be Liverpool's aim. Take the more complete player who is more progressive on the ball and can read a situation better.
If you have followed LFC closely over the years you would know that their achille heal is their defending against physical team and on set plays. From memory they always struggled and only VVD could manage these physical teams. No mater how you bring that up 3pts whatever team you play against is very important. And they have dropped so many easy/cheap points over the years for that specific reason.. Even your B&H team has bullied the LFC backline the past few years on set plays. If you play against the city or chelsea team you can start Gomez but when you need extra physicality you can have Phillips to help.
As for reading situation, Kabak is anything but that. Many times even in his short spell at LFC he has shown poor anticipation and created prime chances for the other team. I don't care if you can make longer passes, the primary goal is to not concede goals and Phillips is way better at that. Obviously he would be a 3rd or even 4th option but he is clearly ahead of Kabak in my book. No need to use the buy option.
Heck just last year, Liverpool lost their perfect record for that specific reason when Deeney man handled Lovren physically and helped creating the key goals for Watford.