Okay you answered the question. Basically through the use of covert devices, like sting ray towers, they were able to intercept communications between the phone and tower. This is not the same as Hacking the device and more akin to wiretapping.Through the phone number the were able to intercept messages which gave them the needed information (IMEI, SIM) to access devices camera/microphone/gps. They implied they were able to then access all major phone manufactures, iphone/samsung/... I am going to believe them, and Snowden. My IT experience tells me, anything can be hacked, if it hasn't yet, it is a matter of time. There is a major benefit to hacking current iphones, so hackers work on it. The likelihood of the average person being hacked is slim to none, we simply have nothing a hacker would need.
Now if the question was, is it possible to eavesdrop in on my conversations; that is a different answer.