A page ranks on desktop but not mobile usually because the mobile version is deficient in Google’s eyes, or because the mobile search results are simply a different battlefield. Under mobile-first indexing, the mobile version of your page is what Google actually indexes and ranks, so anything missing or degraded on mobile costs you directly. The pivot is mobile-version-deficiency or a different-mobile-SERP, and it is observed behavior worth verifying on your own pages rather than assuming desktop and mobile rankings should match.
The deficiency side is the most common and the most fixable. If your mobile template drops content, hides text behind taps Google does not expand, or strips out internal links that the desktop version shows, the indexed mobile page is thinner than the one you think you published. Slower mobile load times and weak Core Web Vitals add drag, because mobile speed is judged on real-world conditions that are harsher than a desktop connection. Cramped layouts, tiny tap targets, and intrusive interstitials hurt mobile usability, and a page that frustrates mobile users is a page Google is less eager to rank for them.
The second cause is the SERP itself. Mobile and desktop results are not the same page rendered narrow; they often differ in which features appear and how much room organic results get. Maps packs, large featured snippets, app results, and other elements push organic listings further down on a small screen, so the same rank position can be invisible without scrolling, or your page can genuinely place lower because the mobile result set is composed differently. What looks like “not ranking” may be ranking buried beneath features.
To act, start by checking parity: view the page as Googlebot sees it on mobile and confirm the content, links, and structured data all survive the mobile render. Then test mobile speed and Core Web Vitals and fix the worst offenders. Finally, search the term on an actual phone and look at the live mobile SERP to see where you really sit and what is crowding you out. Close the parity and speed gaps first, because that is where most of the lost mobile ranking lives.