The idea is to transform the mechanical energy of the wheel into eletric power. For this we used a dynamo, a device that does exactly what we needed. Then some wires are connected to the dynamo, and a chargeable power bank, in order to transfer this generated energy. When the phone charger is connected to the bank, the phone battery begins charging.
In my case, I had a 2,4 Watts dynamo, with a maximum output voltage of 6V, and amperage of 0,4 A. With this output, the battery is charged at a very low rate, but it charges!
Note: each minute in the power cycle, equals 12 seconds of usual charging.