Will apple replace my iPhone 5?

First of all, this can't have been caused by a case since I keep my phone in a pouch...
I got my phone on launch day but this problem has only developed recently; the lock button doesn't always work. Sometimes nothing happens when its pressed, sometimes the display flashes on/off quickly (or vice versa) and sometimes the display will turn on but with no backlight ?!
Knowing my luck when I turn up at the Genius Bar the phone will work fine (it does about 1/3 of the time), so if I explain the situation do you think apple will replace it?
Thanks.