If a key is stored on your phone, it can be obtained the same way any other data is obtained. If the key is password protected, a key logger would yield the password.
Edit: I forgot to check to whom I replied; "lern_to_spel" shows up on all of the Snowden threads.
The keys aren't stored on the phone - that's what's caused all of the recent controversy. A warrant to install a keylogger isn't very useful after the suspect has been taken into custody.
Edit: I forgot to check to whom I replied; "lern_to_spel" shows up on all of the Snowden threads.