Source: Sega Japan Business Agreement Preventing PSO2 Western Release

So how can an animated work based on one of Sega’s most successful game franchises at the moment come to the West, but the game itself still hasn’t?

Anyone who works in contracts and contract law knows it can be a weird, wacky world. And according to a source who spoke to TSSZ, it is one single agreement that, to this point, has prevented Phantasy Star Online 2 from coming to the West. That agreement, our source says, is between Sega of Japan and a Chinese company, and it allegedly prevents Sega from releasing the game onto Steam anywhere for an unknown period. Though not its only means of distribution in the West, Steam is Sega’s primary means of commerce in the PC arena.
The source does not know for how long that agreement is active, but indicated it is finite–but even when that contract expires, it will not necessarily guarantee a path to a Western release. Phantasy Star Online 2 was first released in 2012. A release in southeast Asia, including an English language version, began rolling out in 2014.

The source did not name the company involved on the other end of the agreement, but after some research, we believe it may be Gamania Digital Entertainment. Gamania is headquartered in Taiwan with business ties in mainland China. While Asiasoft oversaw several aspects of PSO2’s launch in southeast Asia, Gamania was tasked with the rollout in the Chinese territories of Taiwan, Hong Kong, and Macau, according to this Famitsu article.
Gamania even produces localized PSO2 trailers as new content arrives. Here is one from 2013, in which PSO2 producer Satoshi Sakai wishes fans a Merry Christmas:

Meanwhile, one more Christmas has passed in the West with fans wondering if they will ever see a localized version of the RPG they have waited too long for.