In the browser extension version of the Phantom wallet, you can view top and trending NFT collections by visiting Phantom's Explore. To get here, first select the 🌐 icon along the bottom of your wallet view and then clicking on Collections.
From here, you view various NFT collections on their respective networks (Only collections that appear on networks that Phantom supports will be listed here). The Top and Trending options (selectable via the drop down menu) contain a list of the top 10 NFT Collections based on volume. Finally as a safety precaution, you can simply click on any of the collections to be redirected to their page within their respective marketplaces. This prevents you from falling for attempts to scam you with incorrect links.