I’m having this same issue with an iPhone SE (my poly firmware is 2.04). At first it could sometimes connect to the iPhone hotspot, but would drop connections frequently. Now I’m seeing the same thing as described above. The phone hotspot may or may not show up in the network list, and if it does, it shows no signal, and you can’t connect.
I can connect to it from a bunch of other phones and laptops, so the issue is likely with the poly.
In any case, I’m using poly in hotspot mode and that seems to work fine, using the hybrid mode described in this forum to remove the routing address so the iPhone can still use LTE while connected to poly’s hotspot