That's for sure a factor, and I should probably care less about judgement (thanks) although I've mainly attributed my stuttering in those situations to the fact I have to say something unexpected. Other examples are when I need to correct myself (I get stuck in something like a loop of "actually no"), or when I say I need to hang up and call back later. I also often find it difficult to say "goodbye" to people without first acquiring eye contact, or in general to say something to people while they are doing something else and haven't noticed me approaching.