Why does my website look tiny on a phone?
Without a viewport tag, a phone assumes the page was designed for a desktop and shrinks the whole thing to fit, leaving visitors pinching and zooming to read. The tag is one line in the page head that tells the phone to use its real width. Every modern theme includes it; its absence means the site predates mobile design or the theme has been edited by hand.
Why it matters
More than half of visits to most business sites are from phones. A page rendered at desktop width on a 400-pixel screen shows text a millimetre high and buttons too small to tap. Google ranks sites by their mobile version first, so a page that does not work on phones is penalised in every search, on desktops too. It is also the first thing Google's mobile-friendly test reports.
What the tag does
The line is: <meta name="viewport" content="width=device-width, initial-scale=1">. It tells the browser to lay the page out at the device's real width and not to zoom out. From there the stylesheet's responsive rules can rearrange the layout for the narrower screen. Without the tag those rules never trigger, because the browser believes the screen is 980 pixels wide.
How to check
Our check looks for the viewport tag in your home page's head. Google's Lighthouse tool and Search Console's mobile usability report flag the same thing, and simply opening the site on a phone shows it immediately.
How to fix it
Add the tag to the head of every page. On WordPress it belongs in the theme's header.php, and any theme built in the last decade already has it, so its absence suggests a very old theme, which probably has other problems and is worth replacing. On a hand-built site, add the line to the template. Adding the tag to a site whose stylesheet has no responsive rules will make it lay out at phone width but not reflow, so the stylesheet may need work too.
Not sure how your own site does on this? Run the free check: it takes about twenty seconds and reports on this and thirty other things.