Don’t give them advice
Comments such as “Slow down”, “Take a breath”, or “Relax” are not helpful and are more than often demeaning. Remember that stuttering is not caused by psychological factors such as stress or anxiety.
Don’t finish their sentences
While you may be tempted, don’t fill in their words or finish their sentences. This will be seen as a sign of frustration and will discourage the person.
Speaking in an unhurried manner will allow the person to feel more at ease in the conversation. However, do not speak slowly to the extent where it is unnatural. Again, this may come off as demeaning.
Maintain eye contact
Mannerisms such as maintaining natural eye contact lets the person know that you are listening attentively to what they are saying, rather than on how they are saying it.
Waiting patiently until the person has finished will allow them to say everything they wanted to. Do not show frustration towards them, or tell them to “Hurry up”. Remember that extra patience will be required when speaking to someone who stutters on the telephone.
The Stuttering Foundation 2015, 6 Tips For Speaking With Someone Who Stutters, <http://www.stutteringhelp.org/6-tips-speaking-someone-who-stutters-0>