How can I setup wireless backup to my Mac with no cable?

You only need to connect the phone to the Mac using a cable the first time that you want to backup.

At that time, you can enable the option to have the Mac recognize the iPhone over Wi-Fi. Once that is done, on subsequent backups, you will be able to back up the iPhone over Wi-Fi to the Mac.

You can’t. In order to set up WiFi syncing or backup, you need to connect the phone to the Mac with the cable.