Your smartphone and most applications are spying on you. Based on watching people use smartphones and asking them about application usage, the iPhone is the worst but Android smartphones are a close second because Android smartphones outsell iPhones by a hug amount and have more applications available.
Occasionally journalists write articles about spyware on iPhones and act surprised when they find out how often every application reports your activity back to their head office.
Location, location, location
Every application and game tries to track your location because that is the most valuable data the application developers can sell. The simplest way to kill that spying is to switch off the phone's location when you are not using the location.
The next step is to delete every application you do not use. The average Android phone has 10 ~ 20 unused applications. Iphone owners often find more than 50 because they load so many applications just to try them out.
For the small number of applications you keep, look at their security settings and switch everything off. No location, no listening to you through the microphone, no watching you and your friends through the cameras, and no access to your data. When an application really does need access to something, switch on only that access. Do not believe any of the pleading messages produced by the malware portion of each application. Only authorise what you specifically need.
As an example, you might have an application that can transmit photographs. What does it need access to the camera? You use the camera application to capture images, not a data transfer application. Why would either of them need the microphone?
One reporter was surprised at the activity created by the Chrome Web browser. How can that be a surprise when it was heavily publicised many years ago and is the major reason why smart people do not install Chrome or use Chrome.
Google released Chrome as a virus infecting computers all over the world through a malware link on the Google search page. Google faked fast speed by preloading pages without your permission. That also faked the statistics about Web browser usage by making Chrome appear to be many times more popular than what it is.
You visit one page using Chrome. Chrome finds all the links on that page for other pages then loads the other pages in the background. You think you are visiting one page but Chrome is visiting 5 pages or 10 pages or 20 pages. You pay for all of those pages through increased data charges. Google sells adverting on all of those pages, increasing Google's revenue.
One of those pages you never visited might feature Russian mail order brides or something illegal or terrorist related. Anyone looking at your machine can look in the Web browser cache and find that page. Everyone looking through the logs of the many servers out on the Internet can see all your page requests. You are so close to major problems every time you use Chrome.
Firefox and some other Web browsers have the same option but it is switched off by default or the Web browser requests your permission, during installation, to perform the scam.
Use Web sites, not applications
You want to book a flight to another city. During the busiest days, I flew only two or three times a day. Why would I use a stupid application to book flights when I know that the application will deliberately limit my choices to the brands paying the highest commissions.
A reported expressed surprise that a travel application constantly contacted a foreign server all day and night. Apparently the reporter had missed the thousands of reports about those applications tracking location to sell advertising for cafes and establishments you really do not want to visit.
Delete those applications. If you are so addicted, you cannot delete an application, disable the application while you sleep. You can disable all of them by switching the phone off overnight. If you use the phone for an alarm, switch off all network and data connections. The flight mode option might be the quickest way to kill the spyware transmissions.
Apple, Google, Microsoft
Look at the reported figures. Apple, Google, Microsoft, all the big corporations are tracking you in far more detail than the CIA, China, NSA, or Russia.
Look at replacing the operating system
Android is based on Linux and that Apple OS is just Unix with technicolor wallpaper. There are cleaner versions of Linux for smartphones. The clean operating systems are still in early stages where installation can be difficult. If you find some with the same phone as you and some experience with a clean OS, you could make the switch and enjoy privacy for the first time.
Delete everything you do not use. Switch off every permission an application does not need. Research an application before installing the application and before continuing to use the application. Use flight mode when you sleep or switch off the device completely.