How to increase current of wireless mobile charger?

I had made wireless mobile charger circuit posted in best engineering projects, but the problem is low current. The current output is about 250mA at 5V which is much less to charge any mobile. I want to increase output current do you guys have any solution.
I had attached my prototype with circuit diagram.

the link of website is
https://bestengineeringprojects.com/...rcuit-diagram/

Increasing the 12V supply will increase the current through L1. Maybe you've got some significant coupling loss, too?