I hardly ever use my iPhone as a phone anymore. But as my eyesight deteriorates, I use it all the time to photograph small-print labels, then pinch and zoom on the photo so I can actually read the text.
Well, what a dope I am. Core77 reader Ross Oliver learned of my plight and wrote in: "iPhones have a built-in magnifier, no need to snap and pinch. Works even if the phone is locked. I find it particularly useful for reading the infinitesimal serial numbers on servers in the data center. Some Android phones have this built-in also, others you need a magnifier app."
9to5 Mac has visual instructions for how to set it up. (In a nutshell it's Settings --> General --> Accessibility --> Magnifier.) Now all I have to do is click the home button three times--that's side button on an iPhone X or later--and voila, I can read whatever I need to. You can even increase the zoom, change the colors for better contrast, and snap a photo if you need it.