iPhone uses Apple's triple-finger-tapping feature to increase the font size for people with limited eyesight. While the feature is great, it seems to have at least one very negative impact on iPhone. I just used it on Google Maps by mistake and didn't notice anything special - before the auto-off turned off the screen. When trying to reopen the phone, the opening screen was so large that the security code entering keypad was invisible and screen could not be scrolled so I couldn't enter my code at all. Rebooting did not change the problem. From Apple support I finally found out that I need to use iTunes to remove this: after connecting iPhone, in iTunes go to general and click Universal Access Options quite at the bottom => for title "Seeing" select "neither" and then "OK" => triple-finger functionality is blocked and the opening screen size returns to normal. No other way to reopen your phone if you do the same mistake as me...