Can anyone comment on whether or not Amtrak trains stop at stations were nobody is getting on or off and there are no staff there to sell tickets at the station? I remember looking out the window at this station thinking that there was only a roof over a concrete slab there. That is the kind of station that I don't know if Amtrak stops at if nobody is getting on or off.
https://www.amtrak.com/stations/wgl

If the stop is not a luggage stop, then there might not be any staff at that stop. And if you are the only person getting on the train at that stop but have not yet bought a ticket, I do not know if the train would stop there or go past at 30 mph while you wave to them. That would be my concern about not getting a ticket in advance if there are no staff at that stop.

If you have no cell service but have a pay phone, I assume you can verbally buy a ticket, I have bought tickets verbally from Amtrak years ago by phone.