Insecurity has several linguistic calling cards, and learning to spot them may help you both assuage others and more skillfully present yourself to the world. People at the edges of a given group are more likely to use language that emphasizes their membership in the group. Central figures are less likely to assert their belonging. Also signs of insecurity: a focus on the pronoun "me", borrowing prestige by using a different conversational style, and hypercorrection.
Just having a feminine voice means you're probably not as capable at your job. At least, studies suggest, that's what many people in the United States think. There's a gender bias in how Americans perceive feminine voices: as insecure, less competent and less trustworthy.