Clark Kent changed his clothes in a phone booth only one time, never in the comic books
Yes, Jerry Siegel and Joe Shuster (creators of Superman) used a phone booth for Clark Kent to change into Superman in a Sunday newspaper comic strip in late 1942. Clark, seeing that there is a job for Superman, excuses himself from Lois by arranging to be called away by a bogus phone call. While inside the phone booth he says to himself, "This definitely isn't the most comfortable place in the world to switch garments, but I've got to change identities - and in a hurry!" Yet this was not the very first time Superman found himself changing clothes inside a phone booth.
Bud Collyer, who voiced Superman in the 1940s radio series, would also sometimes state in an episode that he needed to duck into a nearby phonebooth for a quick change from his Clark Kent identity into the colorful garb of Superman.
Some of the earliest examples of Clark Kent using a phone booth to change in to Superman in the comic books are "Action Comics #119" (1948) in the story "Superman for a Day!" by Edmond Hamilton, "Superman #60" (1949) in the story "Superman Fights the Super-Brain" by Don Cameron, and in "Superman #69" (1951) in the story "The Prankster’s Apprentice" we see Clark removing his shirt in a phone booth.
(text stolen from
Superman Homepage)