Different mobile devices have distinct voice assistants/virtual assistants. As a business, you need to find best practices for VSO. You need to understand the intention behind the voice searches to optimize for voice search for mobile phones. So far, there are four search intent we know.
By understanding the intention behind user questions, you can optimize your content. You can integrate relevant keywords to attract virtual assistants and users (Google Assistant, Apple Siri, Amazon Alexa/Echo, Microsoft Cortona, Google Home Mini, etc.) on mobile phones.