Firstly, huge respect. It's not easy to have a business as a person with you know what. I can relate to it. Having worked as a content writer and illustrator, I would like to have run a remote digital marketing agency but phone and video calls make me think otherwise. Emails and text help but it's not the same. I think clients would like to hear and see the person they would want to give their business to. It's also easier for them to explain their requirements. I would say, to be honest, if you can switch words, use "um", and "like", do that. On phone, they can't see you struggle, so that's a plus. For long-term, I would advise you to work on building a complete new voice. Because I believe stuttering is a bad habit. Rather than correcting an old habit, why not create a new voice? One that's strong, resonant and attractive. Rather than a speech pathologist, I would recommend a vocal coach. Even 90% fluency is a good number to aim at. It will help tremendously in your business. Good luck.