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

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