Phantom dark energy (w<−1) can produce amplified cosmic acceleration at late times, thus increasing the value of H0 favored by CMB data and releasing the tension with local measurements of H0. We show that the best fit value of H0 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 H0+30.93w−36.47=0 (H0 in km sec−1 Mpc−1). This equation is derived by assuming that both Ω0mh2 and dA=∫0zrecdz/H(z) remain constant (for an invariant CMB spectrum) and equal to their best fit Planck/ΛCDM values as H0, Ω0m, and w vary. For w=−1, this linear degeneracy equation leads to the best fit H0=67.4  km sec−1 Mpc−1 as expected. For w=−1.22, the corresponding predicted CMB best fit Hubble constant is H0=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 Ω0mh2 is fixed. We verify the above H0−w degeneracy equation by fitting a wCDM model with fixed values of w to the Planck TT spectrum, showing also that the quality of fit (χ2) is similar to that of ΛCDM. However, when including SnIa, baryon acoustic oscillation, or growth data, the quality of fit becomes worse than ΛCDM when w<−1. Finally, we generalize the H0−w(z) degeneracy equation for the parametrization w(z)=w0+w1z/(1+z) and identify analytically the full w0−w1 parameter region (straight line) that leads to a best fit H0=74  km sec−1 Mpc−1 in the context of the Planck CMB spectrum. This exploitation of H0−w(z) degeneracy can lead to immediate identification of all parameter values of a given w(z) parametrization that can potentially resolve the H0 tension.