I have an awful memory too. I feel like people view me as really "slow" in general when talking, as alot of times it looks like I zone out of conversations or forget what I'm about to say but it's actually the opposite. Its like I have so much to say and I can't get it out, and I can physically feel my body go into over drive in an average conversion so my memory also doesn't help with the way people see me. It could've just been a one off thing with your voice call as everyone stutters once in a while, but it's good your noticing it incase it increases. Mine started small - barely unnoticeable, and even though its still quite small, if you spoke to me enough in person you'd DEFINITELY notice. It could've simply just been a sudden lack of confidence during the conversation you had, but for it to have stuck with you for days after definitely sounds like some sort of social anxiety. I really wish I could help as I understand you completely but I really don't know what else to suggest :/