If we are obligate symbionts, organism plus extended phenotype, so what? What earthly difference does it make to anything?
It explains an aspect of the otherwise puzzling lives of human beings; how insentient things enhance our inherent stupidity (we have highly intelligent qualities as well, of course).
We walk down the street. We pass people apparently shouting intimate details of their private lives to the empty air. Twenty years ago we would have perceived them as insane.
Someone has driven a large vehicle to the end of a narrow, rocky track. They sit in the cab staring around them helplessly. They curse, obscenely, syntactically, at length, apparently threatening the destruction of some invisible spirit. Twenty years ago we would have thought they were deranged.
Two primping idiots, each the very acme of the faults of our species, threaten quite plausibly to destroy the other’s population, and severely damage Earth in the process. Jenghis Khan might have been impressed with the weapon that backed up the threats of these feeble monsters, but Jenghis, whose own contextual extended phenotype not only rained death on nations, but also became a great civilisation, might have been concerned about the pea-brained nihilism that had its finger on the button.
The mobile phone, GPS and thermo-nuclear missiles are all realisations of our extended phenotype.
Jerry Coyne here https://whyevolutionistrue.wordpress.com/2017/08/17/robert-sapolsky-talks-with-sam-harris/ promotes an interesting discussion of free will. I think that the question itself is meaningless, an unfortunate outcome of Reformation theology when the question was raised, if God is omnipotent and omniscient, then he will know everything that is ever going to happen; so everything Is predetermined. So what’s the point?
In the absence of a creator god, the question disappears. However, while the symbiosis of organism and extended phenotype which is us is far too complex for any imaginable determinism, it is a little careless to entirely ignore the influence of the extended phenotype, the technosphere, on our lives and the life of our species.