Phone charger detection

I want to be to detect if a phone is placed on a wireless charger pad. How to detect placing and removal of the device? Probably monitoring current in some way?

Do you have access to modify the pad?

Can you put a weight sensor like a switch on or under the pad?

Is there an Arduino involved in this project?

Yes, I am able to modify it. I want to mount it in a case, so a phisical switch is not an option.

(I am building an amplifier, using an arduino for switching inputs/outputs/channel selection/display lcd and I want to be able to put a phone on top of the case of the amplifier to be charged, and if possible show a message on the display when it is charging)

Why is a switch not an option? I don’t mean a big toggle switch, I mean like a tiny little button that’s pressed by the weight of the phone.