The “Blocked” error appears on the Smartphone tab of the URL Errors section of the Crawl > Crawl Errors page. If you get the "Blocked" error for a URL on your site, that means that the URL is blocked for Google’s smartphone Googlebot in your site’s robots.txt file.
This may not necessarily be a smartphone-specific error (for example, the equivalent desktop pages may also be blocked). However, it often indicates that the robots.txt file needs to be modified to allow crawling of smartphone-enabled URLs. When the smartphone-enabled URLs are blocked, the mobile pages can’t be crawled and because of this, they may not appear in search results.
If you get the “Blocked” smartphone crawl error for URLs on your site, examine your site’s robots.txt file and make sure that you are not inadvertently blocking parts of your site from being crawled by Googlebot for smartphones.
how to resolve and update Robot.txt for smartphone too