Standing waves

V & I r in phase in a perfectly terminated tr line. but when the tx line is open or short circuited, standing waves r formed, and

V&I are out of phase. Why does this happen?

at the short, you cannot have voltage but current is max. at the open, you cannot have current but voltage is max. therefore, out of phase.

It is impossible to define the phase of a current or voltage with magnitude zero, so the statement does not hold.