With Magnifier for Safari you can adjust the font size of Safari mobile to make it bigger and easier to seeIf your eyesight fails or if your father cannot read the letters on the iPhone, you just have to press the share button on the bottom bar and the new option "adjust font" will appear. When you press it, a slider will appear from where you can control the size .
You can download it by $ 0,99 in Cydia.
You will find it in the BigBoss repo.
You need to have done the jailbreak.