I have lived through many emergencies where city power lines are down for days, and eventually my cell phone dies for lack of power. You can use an automobile Cigarette Lighter charging cable to power the cell phone from inside the car, but if someone calls you, it becomes incovienent to sit inside
the car waiting for a call. So, if you get a Car Battery Topper Solar Panel (the kind sold at Costco, for $20 that is used on the car's dashboard and plugs into the cigarette lighter to keep the car battery topped off) you can also place this battery topper panel in any window inside your house where there is direct sunlight, and plug the cell phone's cigarette lighter charging plug into the solar panel...
You will need to get one more thing, an adaptor plug for $3.50 from O'Rileys Auto Store that has a matching plug that fits the solar panel's plug on one end, and has a female cigarette lighter socket outlet on the other end. With this simple adaptor, you can then plug the cell phone's cigarette lighter charging cable directly to the 12 volt solar panel.
I have already set one up for my wife's cell phone, and it works good. The cell phone came alive when I plugged the cell phone into the solar paneI put the solar panel in direct sunlight. The phone's LED screen came on with date and time, and the red charging light also came on, then, after about an hour, the red charging light turned green, which indicated the phone was fully charged.
When clouds came over the sun, the cell phone quit charging, but came back on when the sun came out again.