The CanIt web interface is designed with Web Standards in mind, so the interface should work fine on any device. That being said, there are some considerations to keep in mind while using mobile devices.
Some mobile devices, specifically those running iOS will automatically capitalize the first letter in any given text field. This includes both the login field and the Change Streams field. The trouble with this is that CanIt streams are case-sensitive and so logging in or changing streams with a misplaced capital will land you in a stream that does not exist.
How to avoid this behaviour
Admins can change the Setup->User Lookups entry that they are using for authentication to have the "Force user name to lower-case?" parameter turned on. This will allow users to log in with any combination of capital and lower-case letters. This will, however not help with changing streams, but that is only a concern for the admin users themselves.
iOS also allows you to turn off auto-capitalization. The setting at the time of writing (in iOS 9) is Settings->General->Keyboard->Auto-Capitalization.
Alternatively, if you don't want to disable this feature, you should be able to add a one letter prefix, type the rest of the name, then scroll back and delete the initially capitalized first letter. This is somewhat tedious, but unfortunately we have no way to override the behaviour of these devices.
Small Screen Size
The CanIt WebUI does offer a simplified UI for phones and tablets. Unfortunately this view is only available using the default theme: RP-Web. If you are using this theme there should be a box at the bottom labelled "View" that you can use to switch to "Mobile". If you are not using this theme, you will first have to switch to it using the "Theme" box that is also at the bottom.