Fundamental Question on Bitcoin: How would one convert his "bananas" into bitcoins?
how would one transact his/her hard money or the farm
  products (say bananas) 


It is not possible to transact/transfer/convert bananas to anything else. The same situation is with any other things in real and online world. 

So, if you have bananas you have only one possibility: exchange them for something to a neighbour. Give me your bananas and I will give you my old shoes. If we are far away to each other, we should construct a chain of exchanges: you sell your bananas to somebody (exchange for your local money), he delivers bananas and sell them to me (exchange for my local money).


  using a basic phone without any banking facility?


We do not need phone and banking at all here. But if you want to use a phone in this chain of exchanges, you may have it in your pocket.