Connecting two motors
It is possible to increase voltage by placing them in series.

The output generated can be seen as batteries. When batteries are placed in series the voltage stacks. When placed parallel the voltage stays the same but you can get a higher current from it.

Now if you want to charge a phone by USB you will need a steady 5 volt power. the easiest would be to use a simple 5V ldo so that you wont blow up the phone with a voltage that is too high.

Because some phones have a protection circuit to stop charging when an unstable charger is used, you will need Extra buffers.

An other option would be to use a booster circuit. this will boost the voltage to the required voltage. but you would still need the buffers. There are converters that can work with an input voltage of 1.8-15V and convert any of these to 5V. The output current is dependent on the input voltage/current