Sadly no. I want the same thing. I have to use my phone as a hotspot to stream on my TV and my phone can't see my TV at the same time.
Yeah it does come down to you needing both items sharing Wi-Fi or or if you have a slightly older Samsung it has a option right in the toolbar and when you use it to screen mirror after having working once of your hotspot it will through the toolbar slide down from the top of your screen once hit with no hotspot or Wi-Fi will let you know of a issue to which you reply proceed anyway and it will still mirror sound and all
https://support.roku.com/article/115001480188
Try doing the instructions at the above link. Hopefully this will help