Nothing in life is guaranteed (except death) but FADEC controls on big jet engines are built and tested to withstand electromagnetic radiation (both radiated and conducted) way in excess of anything that's required in industry.
It is obviously completely impossible (short of a strip search and confiscation) to make sure nobody on board has a mobile phone which is switched on. Or has some other electronic device which is radiating.
That said, I have far less faith in GA electronics than I have in the big stuff. I am an electronics engineer (35+ years' experience) and a lot of stuff that goes on in GA avionics is atrocious. A lot of the stuff is designed by complete muppets.
A friend of mine is on his
4th Aspen EFD1000, in 3 years. The last one died just outside the 1 year warranty so while they have supplied a replacement they have washed their hands of covering the labour. They suggested that there was a thunderstorm in the vicinity of his flight
So, yeah, there is an awful lot of crap out there, in the GA business.