Patty Baxter realized there was a problem. In 20 years, her working office usually hummed with sales calls. Now, it was quiet, and advertising sales were down. Ms. Baxter identified a reason: Her sales staffs, all under age 35, were emailing clients with their pitches, not calling them on the phone.Younger workers may have mastered technologies that some of their older colleagues have barely heard of, such as photo and video sharing apps, but some bosses wish they"d learn a more traditional skill: picking up the phone. While Millennials—usually defined as people born between 1981 and the early 2000s—are rarely far from their smart phones, they grew up with a wider array of communication tools, such as texting and online chatting. In the workplace, some managers say avoiding the phone in favor of email can hurt business, hinder creativity and delay projects.Stephanie Shih, 27, says phone calls are an interruption. A New York-based company that designs online and paper stationery doesn"t have a work phone. The company says that not having individual phone lines in open-plan areas protects people from unwanted calls, which can interrupt conversations. Kevin Castle, a 32-year-old chief technology officer at Technossus, says unplanned calls are such an annoyance that he usually unplugs his desk phone and stashes it in a cabinet. Calling someone without emailing first can make it seem as though you"re prioritizing your needs over theirs, Mr. Castle says. Technossus"s staff relies mainly on email to communicate, which helps bridge the time difference between the company"s offices in the U. S. and India, he says. He uses Microsoft Lync for instant messaging and video conferencing. Phone calls are his last resort.Businesses aren"t giving up on the phone yet. Many new phones allow workers to receive calls, texts, instant messages, transcribed voice mails and more all in one system and access the phone system through their work computers.