The last icon in the bottom row is 2 gears.  When you click on it, you get 3 options to save your game.  Pick at least 1, even if you need to make a fake Gmail account. (Just write down the password somewhere because nobody remembers the password to their fake accounts).  Phones die, update, get lost, etc.  The last thing you want is to lose you hard work.  If you do need to recovery your farm, just start fresh and after you play the first few levels you can put in your account info.  It will then ask you which farm you want to continue with - your farm or the new one you just started.  Pick your farm. Facebook also likes to disconnect every once in a while, so keep an eye on that as well.  If it is not saved, there is no way to recover it.