I’d guess they want you to scan the QR code on your PC screen with your phone camera to verify your human identity. If you’re already browsing on your phone, your identity would already be linked through that, so no need to scan.
According to the support page (found here: https://support.google.com/recaptcha/answer/16609652) if you are browsing on a phone it will prompt you to click a link to open some kind of Captcha app on the device rather than scanning a QR code.
I’d guess they want you to scan the QR code on your PC screen with your phone camera to verify your human identity. If you’re already browsing on your phone, your identity would already be linked through that, so no need to scan.
According to the support page (found here: https://support.google.com/recaptcha/answer/16609652) if you are browsing on a phone it will prompt you to click a link to open some kind of Captcha app on the device rather than scanning a QR code.