I don’t believe that mobile devices, computers or any other type of device can all be remotely compromised by design at anytime by the government, but the reality is that Software is more buggy that anyone may think, and this is all true down into the firmware and backbone infrastructure of the internet. Some believe that some of this bugs are left there intentionally in order to be exploited by who know they exist, like the manufacturer, the government and ??? So they are not an explicit backdoor, because normally you need to chain them together to compromise a device.
So all the attackers need to do is to find exploits, specially Zero day exploits and chain them together in very clever and imaginative ways in order to compromise remotely or not the security of a device, and this is happening all the time in computers, routers, mobile phones, TVs, IOT devices, Cameras, Medical Devices, you name it 
It’s in the wild for a lot of years a virus/trojan that survives resets of your computer, reinstall of the operating system. To get ride of it you need to buy a new disk.
Also is in the wild a virus/trojan for your home router that let’s the command and control server switch off from the internet all the home users that have their router compromised by it. This is an effective way to shut of regions of a country or even an entire country from accessing the internet(when the % of compromised routers is huge). To fix it you need to replace the router, because a factory reset will not fix it.
Do you want me to continue?