If you registered for the closed beta on PS4 of Phantasy Star Online 2, Sony Computer Entertainment Japan sent the invites out today, so you may want to check the mail address you associated with your Japanese PSN account.
Invite mails include a code to be redeemed on the web store or on the PlayStation store on the console, and unlocks the download of the client that takes 6.561 gigabytes of initial download and grows up to a fairly beefy 37.2 gigabytes for the full download.
It’s worth mentioning that the client won’t appear in your download list when unlocked, but you’ll have to search for it in the library.
While the client is already available, the beta isn’t open yet. It will start on February 25th, and end on March 6th, so you have plenty of time to predownload that big client before the floodgates open.
While Sega promised a western version ages ago, nothing has been announced since, so keep in mind that the PS4 version of the game is exclusively in Japanese.