Heather, this is really old tech. You can buy thermoelectric chips and build your own. http://www.tegpower.com/pro3.htm
Add a .30 cent voltage regulator and you're done. This would recharge your smartphone but you'll be tending your fire for many hours. The third world implications with this thing don't make sense to me. I know missionaries that build serious power-plants, fueled by biogas, that charge big batteries for villages. They don't need itty bitty chargers for smartphones, and they don't fuel their stoves all day.

I've messed with Seebeck and Peltier devices in the past and found them inefficient....but fun. This is why I posted earlier about steam power (what your house runs on now!) For about $10 you can build a simple/tiny steam turbine that will run on barely boiling water and put out a bit more power than a thermoelectric chip. To get 15v out of that chip above, you'd need to have it cook at 500F degrees. Boiling water is 212F, so less heat/fire is required for the same output, for steam. I'm way over-simplifying here but this is why power-plants still use steam and not thermocouples.

Any of these things will require hours of fire to do anything useful....think how long it takes to charge devices when you plug them into your wall. Now, convert that to logs/campgas/esbit tabs, etc.