Nah you need to think about it in terms of computing power compared to each other.
For example a raspberry pi (using as a substitute for a phone) can do about ~100 hashes a second while my laptop does ~2400. That's 24x faster so if it took my laptop 2 seconds it would take a mobile device ~48 seconds.
See the issue yet? :P
EDIT: According to the screenshots of XMRig for android you only get about ~35H/s which means it would take over 2 minutes to pass a captcha on a phone.
For example a raspberry pi (using as a substitute for a phone) can do about ~100 hashes a second while my laptop does ~2400. That's 24x faster so if it took my laptop 2 seconds it would take a mobile device ~48 seconds.
See the issue yet? :P
EDIT: According to the screenshots of XMRig for android you only get about ~35H/s which means it would take over 2 minutes to pass a captcha on a phone.