How to make the lightning port of iphone output 5V power? like OTG on android phones
Your question is vastly answered by: 
https://apple.stackexchange.com/questions/119707/how-much-power-can-be-drawn-from-the-lightning-connector-by-a-external-device


  Since Apple doesn't publicly commit to power levels or even pin
  compatibility on the lightning connector, anyone interested in
  learning how hardware should be designed to work with Apple's dock
  connectors could choose to join the MFI program:
  
  https://developer.apple.com/programs/mfi/ As a developer, Apple will
  provide you with detailed hardware requirements, schematics and even
  technical support. I haven't seen anyone take a current meter and volt
  meter to the devices and post publicly, but wanted to make you aware
  of one official avenue to get this sort of information across all of
  Apple's iOS product line wether they use the 30 pin dock connector,
  the lightning dock connector or some of the other specific iPod
  connectors.
  
  quoting: Additionally, the pin out for lightning connectors requires
  an authentication chip according to wikipedia, so getting power
  out of a lightning device involves software authentication before
  power will flow.
  
  The article describing 8 pins that are active, indicates that when power flows into the phone (the
  opposite of your use), pins 1 and 5 are ground and power respectively.
  However, until your cable identifies itself to iOS, no power will be
  provided.