I guess you are using Voltage Regulator IC 7805. The disadvantage of this IC is that the regulation of voltage is done by dissipating some amount of power, thus decreasing efficiency. In your case the efficiency turns out to be n=(5I)/(9I)=5/9=55%. Given the charge capacity of the 9V battery to be 500mAH, of which only half goes into the cellphone battery of capacity >2000mAH. So you can expect only a charge amount of 10% of the cellphone battery.