Richard Clark, KB7QHC wrote:
"There is a continuum of phase relationships expressed in degrees
between 0 and 360."

We are discussing transmission lines and assuming near perfection.
Indeed the phase of the wave depends on that of the generator when it
was launched and the phase of the generator continues to advance with
time, but a good line enforces its Zo, a resistance.

Terman says on page 85 of his 1955 opus:
"The incident wave on the transmission line can therefore be described
as a voltage accompanied by a current that is everywhere in phase with
and proportional to, the voltage and dropping back uniformly in phase as
the load is approached."

The transmission line treats the wave reflected from a discontinuity
exactly the same as it does the incident wave.

The reflected wave is identical with the incident wave except that it is
traveling toward the generator.

At an open circuit or high-impedance load, there is tto much line
current for the high-impedance to accept gven the limited voltage. The
surplus current must reverse phase and the wave must travel back toward
the generator. There is no change in the phase of the voltage.

At a short circuit or low-impedance load, there is too much line voltage
for the low-impedance to accept, given the limited current. The surlus
voltage must reverse phase and the wave must travel back toward the
generator. There is no change in the phase of the current.

There are two phasing conditions between the voltage and current on an
ideal transmission line, 0 degrees and 180 degrees.

Best regards, Richard Harrison, KB5WZI