A triangular lattice of rare-earth ions with effective spin 1/2 is an ideal platform for investigating the complex interplay between the multiple degrees of freedom such as strong spin-orbit coupling, lattice, crystal electric fields, and geometrical frustration leading to rich physics. Here, we investigate the single crystals of Yb-based triangular lattice $\mathrm{B}{\mathrm{a}}_3\mathrm{Yb}{\left(\mathrm{B}{\mathrm{O}}_3\right)}_3$ using in-depth temperature and polarization-dependent Raman measurements on different crystallographic planes. Our measurements revealed strong crystal field–phonon coupling reflected in the anomalous phonon hardening. Temperature-dependent Raman spectra of the $ac$ and $ab$ planes show phonon renormalization near ∼100 K ($T$*), reflecting changes in low-lying crystal field populations; below $T$*, lattice contraction, orbital overlap, and symmetry mixing modify coupling, producing phonon anomalies. A broadband centered at $\sim 1800\mathrm{c}{\mathrm{m}}^{–1}$ disappears above $T$*, indicating thermally quenched defect-related luminescence via dissociation of defect-bound states. $\mathrm{Y}{\mathrm{b}}^{3+}$ f-f electronic transitions also reveal the characteristic temperature $T$*, with contrasting temperature shifts that reflect exchange splitting, thermal population effects, and strong coupling between localized $4f$ states and the lattice. These results reveal an intricate interplay of lattice, spin-orbit-coupled crystal field levels, and electronic transitions governing the low-energy dynamics.

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• Crystal-field excitations
• Electronic transitions
• Frustrated magnetism
• Magnetic anisotropy
• Phonons
• Rare-earth magnetic materials
• Triangular lattice
• Raman spectroscopy