Many people are under the impression that a larger phone will help them read better. That is not true, if you have trouble reading on a 4" retina display screen now, sooner or later it will also happen on a bigger screen.
A phone should be a phone, pocketable light and agile.
Also it is not true that it is hard to type on a smaller phone, in fact it is easier, apple keyboard does it's magic with autocorrect, believe me I do have large and thick fingers.
Stop justifying an upgrade to a larger phone and start accepting that reading glasses are needed, to use an iPhone SE or a 6" screen.
I'm 54 and my eyes are aging, so I do accept using reading glasses, also to use my watch.
Of course I like playing around with an iPhone 7 or 7 plus, but for me my SE is best