I know that Phil said that he's not gonna play KH Spin off games because he thinks that Square Enix is 'milking' the spin offs to be released before they start working on KH3.
To be honest and fair, the Kh franchise does have a bit of a screwy narrative. Mainly because Nomura did a lot of back writing and reconnecting between the releases of KH2 and BBS. Pretty much everyone who's played the game has said the same thing.
Phil, if you want to understand more story in KH3, i highly suggested playing BBS, i beat it in less then 30 hours, i had lots of fun playing after buying the whole collection for PS4.(Mobile game does not count!)
But if you don't wanna, you can always watch the cutscenes or read the stories from the games. Now i reard the KH3 will have some backstory
The complete story of Kingdom Hearts - Let's Get ready for Kingdom Hearts III