How can I get 3.7V 100mA from the 220V phase line?
Yes, it's possible. Many moons ago Siemens had a touch dimmer IC which got its power supply from the voltage drop across the triac:  

  

So 4 of diodes in both directions in series with the load will give you a voltage drop of \$\pm\$ 3V as a square wave. You can rectify this with Schottky diodes and still have more than 2V left. There are switchers (SMPS, Switched Mode Power Supply) which can boost 1.2V to whatever your charger needs.  


  WARNING The diodes and everything connected to them carry a lethal voltage!