GoodReader is a high quality file viewing app for the iPhone. It supports viewing of PDF and txt files and offers PDF reflow and in-text search, among other features. It efficiently handles large PDFs, even those containing images. Additionally, GoodReader allows you to not only view files within your Box account, but also upload files to it from your mobile phone.
To use GoodReader, download it from iTunes or the App Store on your iPhone. Open the app, then select "Web Downloads," then "Connect to Servers," then Box Enter your name and password, leaving the "Readable Title" field blank, and then press "Add." Your Box account will appear at the top of the screen, and when you select it you will be able to browse all your files and folders. To download a file, simply tap it once, and all your downloaded files will appear in the "My Documents" screen.
To upload files from GoodReader to Box, go to "My Documents" and click the "Actions" button. Select the file(s) you want to upload, then press "Copy." Go into your Box account and press "Paste," and the files will appear there.