It's not quite clear what it is intended to mean. It could be "You call" or eventually "you are called". It could also mean "teach", thus ni jiao , "you teach". In Pinyin, there are too many homophones, and to "disambiguate", one needs to know the Chinese character behind the Pinyin spelling of that word.

Good bit of working out, Turnoi. Good deduction. I can see like Sholmes Herlock or Arsene Lupin you'd eventually work out the colour of his eyes and where he was on Wednesday at 2200 just from a careless 'ni jao'