It is possible that deleted files, if you try soon after they are deleted can be recovered. Not always, and not always all the files, but it is possible. That said, you would have to have your phone hacked first. So unless this has already happened (the phone being hacked) then I wouldn't worry about it. The more you add files to the device, the more what was there before gets overwritten.
If you are really worried you can always "Hard Reset" the device which will wipe everything you have on it, and reset it to its original state.