Base is not a responsive skin. The thumbnail table and the slide pages are a fixed size, no matter what device you're using to view the album.
A mobile browser like Chrome on Android will do its best to show the entire page within the size of the phone screen, but that usually means that text becomes unreadable, and thumbnails get to be too small to see. Firefox on Android doesn't behave the same way - it just forces the visitor to scroll horizontally.
But if you're trying to accommodate visitors with mobile devices, Base just isn't the skin to use. Look for a skin that is fully responsive. Using a phone, try a skin like Gromit, for example - here are links to several demo albums: https://jgromit.com/gromit/
On the skins page on this site, check the search box marked Responsive layout to see which skins work properly on small displays as well as large ones.