BERLIN (Reuters) – Elon Musk’s demand that Tesla staff stop “phoning it in” and get back to the office got short shrift from Germany’s largest trade union on Thursday. The Tesla chief executive waded into the future of work debate by telling staff at the electric carmaker that they must return to the office for at least 40 hours a week or leave the company, according to an email seen by Reuters. The IG Metall union in the German state of Brandenburg Sachsen, where Tesla’s plant is located, said it would support any employee who opposed Musk’s ultimatum. Tesla employs around 4,000 people in Ger…