Not sure if it's because the person on the phone is doing other stuff at the same time or if it's more like eBooks where they cost the same as Paperbacks because "more profit".
Used to work at a Dominos, though it was pre-internet days. Not sure how much online business the typical store now gets, I know I still always call when I order pizza because it's faster than dealing with the website.
Annoyingly at Dominos they now also have an automated attendant answer the call initially, which reads off the daily specials. That's a big reason I don't often order Dominos anymore but instead call a competitor who still has live humans answering the phone.
When I was at Dominos we had a standard of no more than two rings before a person picked up. People would sprint across the store to get the phone before the third ring.
I've definitely eaten some frozen pizza that were as good as or better than the $5 pizza's from Dominos, I'm in Australia, YMMV.
I imagine if this was more profitable than the existing technology - humans placing toppings and delivering them - it would already be done.
I think when Dominos changed from real baking ovens to what they now use (effectively a conveyorized giant hair dryer) there was a marked change. They had to change the dough so it would not bubble, because the point of the automatic oven is that you would not need a skilled person to monitor the baking.
The conveyor ovens do save labor. When you have 600-degree baking ovens stacked in decks, and you have to watch for and pop bubbles and turn the pies halfway through, and the difference between a pizza being "done" and "burnt" is about 30 seconds, it requires an attentive and coordinated person (sometimes two or three if they are busy) to manage it all. But the pizzas taste better.