I’ll admit, this isn’t an area I’m very familiar with but I see a couple of questions in there just to continue what Caliga said.
L5 doesn’t have mechanical / physical keyboard. On that front, you’d have to consider plugging a device to the USB-c port. On the other hand, it does have audio port (and blue tooth), so earbuds and listening to screen reader is easy. In addition to Orca, would any of the web-browser plugin readers help - especially, are there any that plugin to gnome-browser? Unfortunately, for now, there is no idea how those work on L5 - no one has tested them. And the first step would be to try the virtual machine.
According to what I’ve seen, the user interface has been designed to be graphical but as it’s linux based, there shouldn’t be any problem for pure text based use as well. However, I have no idea what that entails in practise for phone use, even if you would use Lynx or what ever.
But more importantly, perhaps, the Librem 5 is distro agnostic, so you could maybe have one of the designated speech distros intalled. Sonar, Trisquel, Speech Arch and maybe any other Debian based special linux distribution that you might know about, since PureOS is Debian based. Although those might need some work on the interface front as it is thouch screen by default (again, maybe additional keyboard might help, even if it’s not as handy as a phone with built in keyboard).