Can you prevent the iPhone browser from reloading pages?
The behavior that you've described appears to be a limitation of the Safari mobile browser. Other users have complained about the Safari Mobile auto refresh behavior on several Apple community forum posts. 

This iFans post offers some explanations and potential solutions:


  This is not a feature... It's a limitation.
  
  MobileSafari keeps website cache only in RAM, and therefore, once it
  runs out of RAM, it'll automatically destroy an entire page, forcing
  the refresh, disguising itself as an auto-refresh feature. You can
  only keep at most 3 pages open at any time... Even the iPhone 4 with
  double the amount of RAM can only keep 5 pages.
  
  You can try a third-party browser that has offline caching, and it'll
  remedy the situation. Or alternatively, use the swap file mod I posted
  in the jailbreak forums and it should work, too.
  
  These third-party browsers have offline page caching as far as I know:
  
  
  iCab Mobile (also supports concurrent tab, which means you can browse
  websites while listening to music on youtube, this is my personal
  favourite) 
  Atomic Web Browser (many useful features, but the interface
  is a bit strange) 
  Mercury (cool browser that looks like a shrunk
  version of desktop Safari)
  


Your choices appear to be:


Use a jailbreak mod to increase the swap file size (hopefully will increase number of pages that can be stored)
Use a third party browser that supports offline caching