IF is a very powerful game. If you want to play it on a phone you need a phone that is made more for gaming. I use a Sony Xperia XA and i can use high graphics and long haul flights with no lag at all. The Samsung galaxy S8 isnt really made for gaming. For a gaming phone you should get the huawei p10. It has high RAM and very high storage.
If you cant get a phone then you can reduce the freezing crashing etc… you can free up your storage a little if your storage is full, especially and big apps you have on your phone. Also when you are flying try plugging your phone in because IF drastically decreaces your batter and the overall system of your phone. If its plugged in it will reduce that. Good luck!