As the name goes, it's the official mobile template built by Tumblr. This template shows up when you visit your Tumblr blog on your mobile device unless you disable it. This is the default theme of Tumblr Mobile app. Unfortunately, the in-app blog doesn't support any other themes than the one Tumblr provides.
Not every Tumblr theme is mobile friendly to provide a consistent design for accessibility, or optical views for readability, and visuality. If you are using a custom Tumblr theme, and if it's not mobile-optimized, we recommend that you keep this template option on for your mobile visitors.
Your custom theme needs to be mobile-friendly before considering to disable this option. The good news is – all our themes are built in consideration for the mobile accessibility. Care to check our themes? We won't bite!
It's easy. Go to your customize page, and open up your advanced settings.
And then, uncheck 'Use default mobile theme'. Make sure you save this setting before redirecting to another page.
Notice that this may take time, but not as much as an hour. If you deleted your theme before, it may take more.
Have any questions? Feel free to contact us at [email protected]!