iPhone 4 32GB, Windows 7
Why do people keep giving answers about Safari MAC browser, when this is about the iPhone??? My NUMBER ONE frustration with using iPhone is how any browser renders text on websites. There is NO WAY I can change the font size intelligently just for the browser!!! The only text you can significantly increase is the iPhone interface text. This is the main reason I am using Android now, even though I love the iPhone for many reasons, but this one is the BIG ELEPHANT in the room that Apple refuses to address to refine this setting.
I had the same issue. I am sure you found the answer but figured I would post if others ended up on this page as I did.
Holding Command and the Plus + sign will enlarge the text and make the page "reflow" so you do not have to scroll left and right. (or Command minus - to make smaller)
I also think the 2 finger zoom should have a setting to be able to do this but the keyboard command is quick also.
Font size on Safari would also be indirectly related to zoom. If fonts are bigger, it would also mean that you need to scroll from left to right.
I use zooming currently. 
Go to Safari Preferences > Advanced>Accessibility.
In safari make font bigger?
