TL;DR:
Is it possible with OpenWrt to connect to the WiFi of the smartphone and also to set the proxy?
The long story:
I have a particular use case where the router must take the internet connection via WiFi from a smartphone connected in turn to another WiFi network. Basically the smartphone acts as a WiFi repeater.
Unfortunately, the only way I have found to make this smartphone to act as a repeater is with an app that creates a hotspot on the smartphone with its SSID and password but in addition to these it requires that the client also set up a proxy that is the smartphone itself.
Schematically:
external_wifi <-- smartphone + WiFi hotspot <-- OpenWrt (must setup a proxy to the smartphone address) <-- internal_lan_devices