This isn't true. Municipal routes can be optimized to serve the majority of people, and then a ride hailing service can be offered to feed off-route users into the fixed-route network. Most transit agencies offer this service, and many offer full-on ride-hailing (example: C-TRAN's "The Current" in Vancouver, WA).

I don't know where this "can't use a phone" thing comes from. ADA requires that transit services above a certain size offer paratransit, but doesn't specify how those rides are booked. I haven't run into anyone who can't make phone calls and can't book rides online.