Term for signal waveform correction or demodulation Let say a periodic signal waveform $v(t)$ can be modeled as:

$v(t) = f(\phi) A \sin(2\pi ft + \psi)$

where $A$ is a constant amplitude, $f$ is signal frequency, $t$ is time and $\psi$ is a constant phase.

While $f(\phi)$ is $f = k \cos(\phi)$, where $k$ is a constant and $\phi$ is a function of time $t$.

Now the signal $v(t)$ is corrected by removing the dependency to $
\phi$ factor i.e. $v'(t) = v(t)/f(\phi)$.

My question: is the process getting $v'(t)$ from $v(t)$ considered signal waveform demodulation ? or undistortion ?

The generic term I can think safely would be signal waveform correction but it would be better if there is a precise terminology.
Demodulation is not accomplished by division...

So, your operation is undistortion, which has the better name signal restoration, in the signal processing context...