The DragonFly has a standard USB plug, to be usually inserted into a standard USB receptacle of a PC / Mac.
An Android smartphone has a micro USB receptacle.
A micro USB plug-to-a standard USB receptacle adapter / cable is required to connect an Android phone with a micro USB receptacle to a DragonFly with a standard USB plug.
A special micro USB plug, i.e. micro USB OTG plug, with "pin 4 / ID connected to pin 5 / Ground" (or "ID pin grounded"), when inserted into a micro USB receptacle of a USB OTG-featured Android phone, will switch this phone to USB host mode, able to interwork with a USB peripheral device like the DragonFly, in accordance with the legacy master-to-slave or USB host-to-USB peripheral communication model.
Such a micro USB OTG plug-to-standard USB receptacle adapter or adapter cable is usually called USB OTG adapter or USB OTG adapter cable.
A list of USB OTG cables:
http://www.head-fi.org/t/595071/android-phones-and-usb-dacs/5310#post_10854839
". USB OTG adapter (ID pin grounded)
Android device > digital USB audio out >> USB OTG adapter (i.e. micro USB OTG (ID pin grounded) plug to standard USB receptacle) + regular USB cable usually provided by the USB DAC maker (i.e. standard USB plug to standard / mini / micro USB plug cable) >> USB DAC >> amp >> headphones
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