Need some help - will this work and how-to?

I am trying to use (2) GL-MT300N-V2 “Mango” travel routers for a special use case.

What I’m attempting to do is use an iPhone’s hotspot feature as the Internet for (1) of the two Mango’s and then use the second to provide a wireless access point, SSID and network with Internet connectivity WITHOUT having to be “tethered” with a USB cable from the iPhone to one of the Mango’s. I need to be able to have the phone provide the Internet, and still have that same iPhone connect to the SSID/network and still be able to utilize LTE on the same iPhone itself. The goal would be to provide Internet connectivity to a Raspberry Pi while still being able to use the iPhone at the same time.

How do I do this? It works with one mango tethered to the phone with a USB cable, but I need it to work wirelessly. How can I achieve this?

When you use phone as tethering, the phone closes its own wifi connection. So problem of phone.

when you tethering your phone to the router, then

want to access your local devices which connected to the router using your phone

you can do it directly. because your phone can access them.

I don’t have the access I need, which is to be able to “see” the Raspberry Pi as an AirPlay or SpotifyConnect target. I’m trying to leverage Volumio on a headless Pi. I want to be able to start Internet Radio streams, or SpotifyConnect or AirPlay streams over WiFi from the iPhone via Volumio. To the best of my knowledge, this is only possible if the iPhone is connected to the same WiFi SSID. This all works correctly if I tether via a USB cable, but this is less than ideal and I’m unable to do it wirelessly. Seems like there should be a way to achieve this.