Abridged Arena Array: Throughout PSU's run, players have sought out the Free Missions with the most efficient EXP gain. The lobbies for those missions would be accordingly packed full as well. In Vanilla PSU, this first happened to "Plains Overlord," then to "The Mad Beasts," then to "Endrum Remnants." When AotI was released, this honor went to "White Beast," and remained so whenever an event wasn't going on—to the point that PSU itself was derisively nicknamed "White Beast Universe" as no one seemed interested in running any of the other missions in the game.
This tendency prompted Sega to introduce the "GUARDIANS Boost Road," encouraging players to run chains of other missions for greater gains compared to spamming a single mission over and over.
Complacent Gaming Syndrome: CASTS and Beasts were more commonly used by serious players (For melee and gun-using classes) than Humans or Newmans due to their Limit Break racial abilities. For TECHNIC-using classes, however, Newmans (particularly female Newmans) were the top pick.
Ear Worm: The sub-series' theme tune, Save This World, in its multiple incarnations. People either adore it or find it ear-splittingly grating, especially the original version from Universe.
Anga Jabroken, in reference to Anga Jabroga's status as a Gamebreaker.
Lolitechers, who are very small Newman female Fortetechers/Masterforces/etc.
Game Breaker: Some weapons and Photon Arts were considered this during the game's run.
Anga Jabroga, an Axe Photon Art, was infamous for being capable of easily wiping out crowds of enemies. It was nerfed later on, though.
Dus Majarra, a Spear Photon Art, was capable of dealing incredible damage during the second attack in its combo. When Dus Majarra was nerfed, it was that part of the combo specifically that was targeted.
Shotguns were also considered this at a point, especially when used by Gunmasters.
Idiot Plot: Episode 1, which resulted from having Ethan as the protagonist.
I Knew It: Many theorized that Hyuga has become a Dewman, which is confirmed in PSP2i.
Moral Event Horizon: Light Master Dohgi Mikuna is revealed to have crossed this a long time ago when Ethan discovers that Dohgi had been using Mirei Mikuna's gifts of divination for rogues and other criminals, receiving payments for doing so. Long before that, Dohgi placed a Mark of Light on Karen, Mirei's twin sister, to bolster Mirei's vitality; the Mark saps Karen of her abilities, which leaves her unable to use TECHNICs. During Episode 1, Doghi attempts to finish the job by sacrificing Karen's life in order to prolong Mirei's. Mirei tries to stop him, but is met with a powerful Technic that kills her.
"Stop Having Fun" Guys: You didn't have to do much to get booted from a party, especially at the end boxes in certain missions.
That One Boss: Magas Maggahna is quite the Lightning Bruiser. It has plenty of powerful attacks, it moves around a lot (and loves to spam its teleport,) it can stop damage with a shield, and breaking its bottom part makes it even harder for melee characters to damage it.
They Wasted a Perfectly Good Plot: A minor example. Importing a character from Phantasy Star Portable to its sequel results in no significant storyline differences. Even characters whom you've met before in the first game don't seem to recognize you, and the only one that does is Vivienne, who's an optional partner in PSP2 (unlike, say, Tonnio and Liina, both of whom are met at the start of Chapter 2 and aren't optional), and even then that only amounts to a couple of changes to her dialogue upon meeting you. The fact that there isn't even an attempt at an explanation for it is also bothersome. As such, there are players that feel that SEGA dropped the ball in this regard, but at least importing still nets you a unique title and some neat items.