You rock! Job interviewing IS work experience, in a sense, it's building up confidence and experience through the interview process. As a person who stutters, I can attest to this by saying it gets easier, and it will. Own up to your stutter and stutter openly, even when you feel you are doing fine, stutter. You shouldn't be embarrassed or apologize, but I know it's hard and I'm guilty of this, too. Instead, work on this: do more calls, do more interviews, and don't worry about your speech. Know you are qualified and right for whatever you set your mind to. You got this. You didn't fuck it up. You grew.