Studies of absorption and luminescence spectra, and luminescence decay times of the intrashell f-f transitions of Y b(³+) ions in bulk orthophosphates at different temperatures and at high hydrostatic pressures are presented. The spectroscopic properties of Y₀.₉₉Y b₀.₀₁PO₄ crystal with a tetragonal zircon structure and Gd₀.₉₉Y b₀.₀₁PO₄ and La₀.₉₅Y b₀.₀₅PO₄ crystals with a monoclinic monazite structure are compared. Experiments at ambient pressure were performed at temperatures from 10 to 295 K whereas measurements at high pressure were performed in a diamond-anvil cell at 10 K with a pressure up to 160 kbar. The results reveal a high thermal and pressure stability of the optical properties of the examined crystals as well as the dependence of Y b(³+) emission properties on the local symmetry of the site occupied by the ytterbium dopant.