1. A memory device having instructions stored thereon that, in response to execution by a processing device, cause the processing device to perform operations comprising: identifying a key phrase that appears in digital content; generating a score for the key phrase based at least in part on view counts of social media content items associated with the key phrase, the social media content items being accessible to users of a social media service; determining, based at least in part on the score, whether to use the key phrase to select contextually relevant content to associate with the digital content; and responsive to determining to use the key phrase to select contextually relevant content to associate with the digital document, storing an indication of the determination in the memory device or another memory device.