  The Debye temperature, T${_\theta}$=(h/2${\pi}$)/k${_B}$$\omega$$_\theta$,
where the Debye frequency $\omega$$_\theta$ is integrated characteristic
frequency of full phonon spectrum, $\alpha$$^2$($\omega$)F($\omega$). In the
BCS theory, T${_\theta}$ in conjunction with electron-phonon coupling strength
parameter, $\lambda$$_{e-ph}$, determines the superconducting transition
temperature, Tc. Despite a fact that more accurate theory of electron-phonon
mediated superconductivity requires the knowledge of full phonon spectrum,
$\alpha$$^2$($\omega$)F($\omega$), which can be very accurately computed by
first principles calculation technique, there is no experimental technique
which can measure $\alpha$$^2$($\omega$)F($\omega$) in highly-compressed
near-room-temperature (NRT) superconductors. Thus, $\omega$$_\theta$ remains to
be the only measurable parameter of full phonon spectrum,
$\alpha$$^2$($\omega$)F($\omega$), which can be deduced by the fit of
experimental temperature-dependent resistance data, R(T), to Bloch-Gr\"uneisen
equation. Taking in account that within electron-phonon mediated theory of
superconductivity two isotopic counterparts (or, in case of NRT
superconductors, the same superconducting phase at different pressures),
designated by subscripts of 1 and 2, should be obey the relation of
T${_\theta}_1$/T${_\theta}_2$=T${_c}_1$/T${_c}_2$, there is a way to
reaffirm/disprove the electron-phonon mechanism of NRT superconductivity. In
this paper, we perform the analysis for R3m-phase of H3S at different pressure,
as well as for several superconductors in LaHx-LaDy system and show that there
is a large disagreement between experimental data and
T${_\theta}_1$/T${_\theta}_2$=T${_c}_1$/T${_c}_2$. Taking in account that
similar disagreement has recently reported in H3S-D3S system, it can be
concluded that primary origin for NRT superconductivity remains to be
discovered.
