Can pho be served ice cold?
A (somewhat south) Vietnamese not currently in Vietnam chiming in ^^ :

Apart from some exceptions (like cà phê sữa đá) I have the impression that there are no traditional ice-cold Vietnamese dishes whatsoever (I'd even dare to say that almost all desserts are eaten warm or at least at "room temperature" at 36°C / 96°F). Maybe it's just due to the non-availability of ice and constant power outrages that lead to cozy 20°C / 68°F in the freezer. What I've also observed is my Vietnamese relatives in Vietnam always want to have their tender herbs / lettuce / mung bean sprouts blanched and served immediately. The reasons are omnipresent nasty pathogens.

(Don't ask me how they eat their bún chả or bánh xèo with lettuce without getting belly-ache. Perhaps it's all about mitigating risk but not completely avoiding it at all costs.)

To answer the question: Probably no. At least not traditional phở.