Sesquiterpene synthase converting farnesyl diphosphate into beta-sesquiphellandrene and six minor products, zingiberene, 7-epi-sesquithujene, sesquisabinene A, (E)-alpha-bergamotene, (E)-beta-farnesene and beta-bisabolene. Can also accept geranyl diphosphate as substrate, producing nine monoterpenes, with myrcene and limonene as the major products. (2E,6E)-farnesyl diphosphate = beta-sesquiphellandrene + diphosphate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Up-regulated by herbivory. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.