Can a workflow create an AI agent from a business's website?

Yes. The workflow builder has a Create agent step. Enter the business's website address and the step builds an agent from that site, which takes about 60 seconds. You can pick the voice and the language.

You can also create and edit agents through the API, for example to attach a phone number to the created agent.

Because it takes about a minute, a good pattern is to create the agent as soon as a prospect replies (for example with the word "test"), so it is ready by the time they click your link or receive a number.