I do agree considering the treatment of property in general. But your statement was:
This may apply to conventional computer like devices. But speaking of “mobile phones” as we do here, I tend to place them among the field of embedded systems.
Here one may still do with it what he want, but if the manufacturer delivers the device with a appropriate OS and everything is matched, optimized, tested and certified in this form one may try to switch the OS, but the manufacturer need not cover such actions by warranty and imho does not violate anyone’s rights by preventing the option to switch the OS.
Prior to each purchase every products feature ought to be clearly described so customers know what they will get for their money. This should also prevent situations where one may unsuccessfully try to flash his mobile, as the option for re-flashing most sure will not be listed specifically as a product feature. Furthermore if one don’t like Google’s Android he probably is keeping the wrong product in his hands. Expecting the option to some day use the source code to modify and re-flash the phone without Google stuff seems to me a bit too high.
At last I also agree with the explanation from @calvofl0.
So who of the few that were trying to re-flash their FP3 can doubtless say that he done every single step just as proper and precise as the manufacturer to get the same result of a working/booting FP3 mobile?
I am uncertain if the GPL part in this case clearly should put each customer in the position to re-flash the phone with the provided source code.
I think there is still much room for verification if the code is incomplete/wrong/broken or the complex procedure of compiling and flashing was not 100% matching.
I believe Fairphone is confident that the delivered source code is complete and usable. But consider this, what about Fairphone asking “individuals” what makes them certain that the code seems wrong, broken or incomplete?