You make do with what you have. Heck, I used to read WAP sites on a feature phone wth a 2" highly pixelated LCD. The primary reason I bought the (original) iPhone is for reading fanfiction (via Safari). Stanza (now-defunct epub reader) kept me locked in to iOS for the longest time (pretty much 5 years worth of reading on a 3.5" display). Interestingly enough, I much preferred reading text on the iPhone 4's ~300+ ppi 3.5" screen than on the iPad 2's ~150 ppi 9.7" display. Wasn't until the iPad went retina that I started using for anything other than manga.
That said, I never could stand reading comics/manga on the iPhone's tiny screen. Just not a fan of guided view. I tend to read in landscape mode (2-page spread). Manga is pretty much the entire reason I bought an iPad. Now that I'm starting up on American comics, tempted to get the 12.9" iPad Pro. While 9.7" makes for a comfy replacement to Japanese tankobons or bunko, it's a wee bit too small for American comics when reading landscape.