Back in high school I tried using my first android smartphone for studies and notes when my laptop had broken down. I connected a (wired) keyboard and mouse, but it got tedious really quick. I guess one can theoretically work off only a phone, but even simple tasks take considerately longer to perform. The only real positive thing was the small carry size and the addition of a touch screen.

Having learned nothing from the first attempt, I later brought only a phone to surveying field work as newly graduated UAS robotics engineer (needing it for route planning, weather stats, auxiliary vehicle integrations, data transfers, etc.), and, well, it could do everything I asked it to do, but it would again have been significantly faster with a proper mobile workstation. Since this was with a phone without USB-C (so no PD hubs) the additional power drain also meant that the phone barely lasted throughout the day, even if I connected it to a power bank every time I did not need it. It also kept overheating in the mid spring sun. I knew that smartphones are bad at heat management, but I hadn’t expected it to be that bad.

At last, I’ve recently had half a year where I’ve used only my phone and a Steam Deck for all my computer related tasks (between jobs, rig was in storage). The SD allowed me to do everything from gaming to light dev work, and the phone was enough for all communication (bank, contacts, E-Mail, etc.) and social network requirements. I guess I could live that lifestyle again for a limited time, but having back my rig is just so much more comfortable, especially for heavier dev tasks.

TL:DR: One can definitely live with only a phone, especially if the lifestyle is less technically inclined, and even a techie can ultimately do most tasks on a phone, but while a properly configured phone can do most tech tasks it’s just so much faster to have proper computer at hand.