How to securely dispose of a smartphone?

How to securely dispose of a smartphone?

How to dispose of a smartphone (it's an iPhone 5) at home? I was reading through this SE site questions and found this one which hardly applies here. Besides, I'd want to do it so that:

• It's not damaging the ecology (at least not too much)
• I don't have to do it with work tools (I don't have a hammer and surely don't want to set anything on fire in my apartment)

The device is currently in use for all sort of things - 2factor auth, custom authenticators, personal data, banks eTAN etc etc.

After the disposal, the data from the device must be impossible to restore and the device should be impossible to use as anything but decoration.