I, too, struggle with one worded syllables at times. Whether it’s on the phone or in person. “Bye” or even a confirming “Yes” gets me. I don’t know what it is, but sometimes it does happen when I get truly nervous or even when I’m chilled out trying to order food at a restaurant with my girlfriend. But you just have to realize that we are all adults, and most people will understand. At least they are aware :) because I try to make people aware after the fact, and they don’t mind it one bit and doesn’t change anything about the friendship/relationship.