Hi dinless,
Welcome to Apple Support Communities! Let's get this sorted out together, so that you're able to use the Speak action without issue.
To ensure we understand correctly, this issue only occurs when using Siri Voice 1. Is this right? What happens if you head into Settings > Siri & Search, then choose a different voice option under Siri Voice, then test again?
For example, what happens when you choose Voice 2, allow it to download if necessary, then test the Shortcuts action again.
Please also let us know which iPhone model and iOS version you're using. The version can be found under Settings > General > About.
Have a great day!