Google uses the mobile version of a site's content for indexing and ranking, known as mobile-first indexing. Based on Google Search Central's documentation, here is what to check on a business site.
What mobile-first indexing means
According to Google Search Central's official documentation, Google uses the mobile version of a site's content to index pages and rank them in search results. This approach is called mobile-first indexing.
A site without a mobile version can still appear in search, but Google very strongly recommends providing one. Of the available approaches, Google recommends responsive design, where a single page adapts its layout to the screen width, as the easiest to implement and maintain.
This article is based on what the official documentation states, and the details may change over time.
Keep mobile and desktop content aligned
The mobile version should carry the same primary content as the desktop version. When screen space is limited, the documentation suggests organizing content with accordions or tabs rather than removing it.
Headings, page titles, and meta descriptions should convey the same meaning on both versions. The same applies to image alt text.
If information such as service menus or pricing tables appears only on the desktop version, Google may not be able to use it when evaluating the page.
Make sure Google can read the content
Google cannot read primary content that only loads after a user swipes, clicks, or types, because Google does not perform those interactions.
Check that directives telling search engines not to index a page, such as noindex, have not been added to the mobile version by mistake. It also matters that robots.txt does not block files the mobile version needs, such as images and CSS.
On advertising, the documentation notes that ads taking up a large part of the top of a mobile screen harm the user experience, and it asks sites to follow the industry's Better Ads Standard.
If your mobile site uses separate URLs
Sites that serve mobile pages from separate URLs, such as addresses starting with m., have more to watch for. Examples given include not redirecting many desktop pages to a single mobile home page, and verifying both versions in Search Console.
With responsive design, content and settings are shared on a single page, so mismatches like these are less likely to occur.
TAKEAWAY
What this means for your project
Open your site on a phone and confirm it shows the same key information as desktop: pricing, services, contact details. Check that important content is not hidden behind interactions, that noindex or robots.txt rules do not differ by version, and that ads or banners do not dominate the top of the screen. If you use separate mobile URLs, discuss moving to responsive design with your developer.