Using an RTG to power your phone isn't a real suggestion. Lithium batteries can last for a day (especially if you're willing to accept a thicker phone) and the inconvenience of having to charge it while you're asleep is minimal. A more realistic application might be something like military radios where you may want them to keep working for extended periods of time in areas where electricity is not available, and then you have an organizational structure that can take care of proper disposal.
The point is that it's not a scaling problem. It's practical to make an RTG that small as a technical matter.
The point is that it's not a scaling problem. It's practical to make an RTG that small as a technical matter.