Converts geranyl diphosphate to four products with (-)-(4S)-beta-phellandrene (52%) as the major olefin, and lesser amounts of (-)-(1S,5S)-beta-pinene (34%), (-)-1S,5S-alpha-pinene (8.5%), and (-)-(4S)-limonene (6%). Involved in defensive oleoresin formation in conifers in response to insect attack or other injury. Involved in monoterpene (C10) olefins biosynthesis. (2E)-geranyl diphosphate = (-)-beta-phellandrene + diphosphate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Terpene metabolism; oleoresin biosynthesis. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). The conserved 62-Arg-Arg-63 motif may play a role in the isomerization step of the terpenoid cyclization reaction sequence. Belongs to the terpene synthase family. Tpsd subfamily.