Stutter when stressed?

Stutter when stressed? I am lucky in that I do not have a stutter on a day to day basis. In most circumstances I am basically fine and do not have any issues but when I am stressed or upset I start to trip over my words and repeats two or three words, I cannot say how long it lasts for because honestly it's never that simply, it just vanishes after a while, it can either be on a phone call or in an everyday conversation. Does anyone have any advice of how to centre? I am thinking if I could find some kind of stress toy or something to focus on it would help. Does anyone have any recommendations?