On October 31, 2023 Google declared mobile-first indexing complete: it "uses the mobile version of a site's content ... for indexing and ranking." Content missing from your phone layout is missing from Google, so serve the same content, structured data and metadata to every device, ideally with responsive design, "the easiest design pattern to implement and maintain."
Two old claims need updating. After "Mobilegeddon" (2015) Google called mobile-friendliness a ranking signal; its page experience documentation now says aspects beyond Core Web Vitals "don't directly help". And AMP has not been required for the Top Stories carousel since 2021.