Elucidating the origin of long-range ferromagnetic order in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>Fe</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:msub> <mml:mi>GeTe</mml:mi> <mml:mn>2</mml:mn> </mml:m

We report a detailed high-field/high-frequency ferromagnetic resonance (HF-FMR) study of low-energy magnon excitations in the van der Waals ferromagnet ${\mathrm{Fe}}_{2.92(1)}{\mathrm{Ge}}_{1.02(3)}{\mathrm{Te}}_{2}$. At $2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the field dependence of the magnon branches is well described by a semiclassical domain-based model, from which we extract key microscopic parameters including the anisotropy gap $\mathrm{\ensuremath{\Delta}}=170(4)\phantom{\rule{0.16em}{0ex}}\mathrm{GHz}$, the anisotropy field ${B}_{\mathrm{A}}=5.85(8)\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, and the effective $g$-factor ${g}_{\mathrm{ab}}={g}_{\mathrm{c}}=2.07(4)$. Furthermore the uniaxial anisotropy constant is determined to be $K=10.50(23)\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.16em}{0ex}}\text{erg}/{\mathrm{cm}}^{3}$. Anisotropic short-range magnetic order persists above ${T}_{\mathrm{C}}$ up to approximately $270\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, as evidenced by a finite anisotropy gap and anisotropic shifts in the ferromagnetic resonance (FMR) resonance fields. Both results clearly show the presence of anisotropic local magnetic fields well above ${T}_{\mathrm{C}}$. Our findings underscore the crucial role of magnetocrystalline anisotropy in driving long-range magnetic order in ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$.