Using a 6s for many years, and he has no backup? I'm loathe to think how much precious data is on that phone, only a theft or accident away from being lost forever.
It's only a dollar a month to have 50GB of iCloud storage, which is more than enough to back up 90% of iPhones. I suggest pointing this out to him so he can back up his phone (which will make moving to a new phone much eaiser) and so his data is safe. Good luck.