yeah reading mangas on phones is a pain, needing proper naming for sequence and zooming to read and all.
however, the higher PPI of phones makes blurry mangas a bit more readable.
honestly though, some readers (both LN and manga readers) have issues with number sequence.
e.g. 1, 11, 12, 2, 3, 31, 4, etc. needs to be renamed to 01, 02, 03, ..., 11, 12, 13, etc.
just keep in mind that iphones doesn't have uSD expansion, so you'll have to resort to using OTG USBs to hold more than the internal storage.
its better to aim for 128GB minimum on this regard, a portion of that is reserved for OS+factory default, so the actual usable space may well be less than 100GB.
PS: i've recently bought an Asus Zenfone Go 5.5", a bit too big to my liking but its quite satisfying so far.
i'm reading mangas and novels from online sites and its doing great, speed wise its on the slow side, but for it's purpose it doesn't matter.