In my jailbreaking experience, this would mean that you're stuck until you get to a computer with iTunes. You can then restore the phone in dfu mode if you can manage to get it to cooperate. Sometimes the iPhone will let you enter it as if you just started your phone from being turned off while in a reset loop.
When you jailbreak you phone, you modify the OS. The iPhone uses the currently-installed version of iOS as its master copy of the OS when you reset the phone. If the master copy is modified, then the iPhone doesn't know how to deal with the anomaly. In this case, iTunes can then be used to flash a new fresh master copy (so to speak).
You might have more luck in the Jailbreaks and iOS Hacks forum or /r/jailbreak, but I wouldn't get my hopes up for a non-iTunes solution.