  Phantom dark energy can produce amplified cosmic acceleration at late times,
thus increasing the value of $H_0$ favored by CMB data and releasing the
tension with local measurements of $H_0$. We show that the best fit value of
$H_0$ in the context of the CMB power spectrum is degenerate with a constant
equation of state parameter $w$, in accordance with the approximate effective
linear equation $H_0 + 30.93\; w - 36.47 = 0$ ($H_0$ in $km \; sec^{-1} \;
Mpc^{-1}$). This equation is derived by assuming that both $\Omega_{0 \rm
m}h^2$ and $d_A=\int_0^{z_{rec}}\frac{dz}{H(z)}$ remain constant (for invariant
CMB spectrum) and equal to their best fit Planck/$\Lambda$CDM values as $H_0$,
$\Omega_{0 \rm m}$ and $w$ vary. For $w=-1$, this linear degeneracy equation
leads to the best fit $H_0=67.4 \; km \; sec^{-1} \; Mpc^{-1}$ as expected. For
$w=-1.22$ the corresponding predicted CMB best fit Hubble constant is $H_0=74
\; km \; sec^{-1} \; Mpc^{-1}$ which is identical with the value obtained by
local distance ladder measurements while the best fit matter density parameter
is predicted to decrease since $\Omega_{0 \rm m}h^2$ is fixed. We verify the
above $H_0-w$ degeneracy equation by fitting a $w$CDM model with fixed values
of $w$ to the Planck TT spectrum showing also that the quality of fit
($\chi^2$) is similar to that of $\Lambda$CDM. However, when including SnIa,
BAO or growth data the quality of fit becomes worse than $\Lambda$CDM when $w<
-1$. Finally, we generalize the $H_0-w(z)$ degeneracy equation for
$w(z)=w_0+w_1\; z/(1+z)$ and identify analytically the full $w_0-w_1$ parameter
region that leads to a best fit $H_0=74\; km \; sec^{-1} \; Mpc^{-1}$ in the
context of the Planck CMB spectrum. This exploitation of $H_0-w(z)$ degeneracy
can lead to immediate identification of all parameter values of a given $w(z)$
parametrization that can potentially resolve the $H_0$ tension.
