Phelps served in increasingly senior roles at Paramount Global, previously known as ViacomCBS, and its predecessors. She rose to a top communications role at Viacom, which merged with CBS Corp. in late 2019. She oversaw Paramount's communications team through the Viacom-CBS merger, the launch of Paramount+, and the corporate rebrand to Paramount Global. Among the initiatives she developed with her team was Spark, a global expansion of BET's Content for Change campaign, and the establishment of cross-company marketing and publicity functions.