The mobile port is just very unoptimized, you need quite a beefy phone to run it. Sorry T^T (that's usually the issue)
It's a common issue, people seem to be solving it by changing their PC's system local to Japanese (as weird as that may sound).
Try navigating to either your C: or D: drives and locating a folder named "MyNewGame", after you find it, go inside and edit "TermineSettings.xml" to get the resolution you want. That should probably fix it?
