Don't forget to make sure it has enough internal storage to hold all of FGO's bloated assets. My old phone would start slowing down every week or so and I had to clear FGO's cache because I was running out of storage, and for whatever brilliant reason you can't install FGO or put its several GB of assets on an SD card.
Pen-chan best girl, she's useful pretty much always, and that's not even counting her anti-greek-mythical-male buff (which admittedly is a bit niche)