Players who have reached the top 500 by the time the phase has ended will be rewarded with a special in-game title. From the sound of it, we won't be tasked with reaching a certain points threshold to obtain Legend, but rather, the 500 players who have the most Master Rate will likely be given the Legend rank. On that same date, players will be able to strive for what will be an undoubtedly highly coveted rank, Legend, which will only be awarded to the top 500 players on the leaderboards. From what we've learned today, it appears the league's next phase will be starting up on November 1.
At this point in time, Street Fighter 6's Master League - the online ranked league that sees Master-level players compete for special 'MR' (Master Rate) points - is currently in phase 1.