If you have the confidence just fiat out say something like "Hey before I start, I tend to stammer quite a bit so bear with me", so that people can understand easier and if you do find yourself stammering it will dramatically decrease the overall awkwardness, and of course confidence and courage is a good attribution to carry. Phone calls are bloody debilitating yes, but you can just point it out to whoever is on the receiving end. Stress and anxiety can really increase your stutter, so finding ways (if you do experience the two) to remedy those will help also. I'm not a professional but I hope my advice helped a little. Keep soldiering on! Good luck to you