Phone privacy matters
Having your personal information leaked can happen pretty easily, but to do so, from the perspective of the one that takes it, is quite hard. That happens always for personal interest or gain, because someone paid for that to be done or as a part of a network of mobile monitoring frauds.
But phone privacy matters, and no one will give it to you unless you make sure to get it. Of course, the simplest and most secure way to never be foxed is to not own or even use a phone, tablet or laptop. That may be much harder than it sounds and it most certainly is the wrong way, so don't think about it and make sure you are protected on other ways. You can find more about that on this website.
Maybe we should return to letters
A few weeks ago there was a legit photo of Mark Zuckerberg, that he uploaded, with him sitting in front of a laptop at the Facebook Headquarters. Sounds normal, but it is not when you consider that the camera and microphone on the laptop were taped so that no pictures, video nor sound could be taken even if the device was monitored. This may sound quite weird, but it is the most secure, and best way to protect yourself from these kinds of phone monitoring.
However, your calls, messages and identity are still reachable, because they are in the phone, being transferred in ones and zeros, so you can't tape them. What you can do is make sure you don't give too much away, take care of how much and where you type in your name, address and phone number. Keep in mind that the best protection against phone monitoring is not letting anything out there that can be monitored.