Rachel is automatically assigned a phone number when she's set up; it's not possible to choose or bring your own custom number at this time.
However, if you'd like calls to reach a specific number (such as your business line), you can enable call transfer in Rachel's settings. This allows Rachel to transfer calls directly to the number of your choice, so your callers still get to the right place.
Want the details on how transfers work (warm hand-off vs immediate, single vs multiple)? See How Rachel's call transfer works.