I suggest forgoing the idea of creating generators/dynamos/alternators and simply going for a simple battery:

Create a Lemon battery

According to sources a single lemon battery cell creates around 0.9V in voltage. If you add 5 of them in series you should get some 4.5V which might be enough. Then simply scale the entire thing up in parallel to increase the current until you reach the needed amperage for your phone.

Needed materials:

• Lemons
• Copper
• Zink
• Wiring of some sort

I suggest forgoing the idea of creating generators/dynamos/alternators and simply going for a simple battery:

Create a Lemon battery

According to sources a single lemon battery cell creates around 0.9V in voltage. If you add 5 of them in series you should get some 4.5V which might be enough. Then simply scale the entire thing up in parallel to increase the current until you reach the needed amperage for your phone.

Edit: I even found this proven in a YouTube video.

Needed materials:

• Lemons
• Copper
• Zink
• Wiring of some sort