Most mobile browsers are not geared towards doing developer-related things like viewing the source code of a page. There’s a nice bookmarklet, however, that will get you this functionality without too much trouble.
To be honest this is an awesome little mobile tool, but you can also use it on a desktop browser. When viewing the source code of a page it scales to the width of the browser, and so it works equally well on a tiny mobile screen or a larger desktop screen.
When using it on my iPhone, however, there’s one thing you need to keep in mind. To scroll the content area you actually need to use two fingers due to the fact that Safari doesn’t put a scrollbar in the box. It’s hardly a deal killer, and as you can see in the screenshot there is a friendly reminder about this when you go to use it.