

I did that with a GL.iNet travel router after flashing stock OpenWRT, and used it as a wireless bridge for several years. It uses relayd to bridge the Wifi station interface and Ethernet. Once you have an ethernet bridge, you can connect another AP or do whatever from there.
If you create a second wifi interface in AP mode (in addition to the station/client one connected to the upstream), you should be able to add that to the LAN bridge alongside the ethernet interfaces. That bridge will then be part of the relayd bridge, and it all should just work (should, lol. I haven’t tested that config since I only needed to turn wifi into wired ethernet with this setup).
Interfaces:
LAN Bridge: Ethernet interfaces to be bridged to the wifi
I have both of its interfaces in this bridge, and it also has a static management IP (outside of the WLAN subnet). This management IP is a static out-of-band IP since the devices connected over ethernet won’t be able to access it’s WLAN IP (in the main LAN) to manage it. To access this IP, I just statically set an additional IP on one of the downstream ethernet client devices.
The LAN bridge is in a firewall zone called LAN.
WWAN: Wireless station interface that’s configured as a client to the AP providing upstream access. I have this configured statically, but DHCP is fine too. Firewall zone is WLAN.
WLANBRIDGE: The relayd bridge (Protocol: relay bridge). It’s interfaces are the LAN bridge and the WWAN interface.
Disregard the WGMesh parts; that’s separate and not related to the wireless bridging mode.
Hmm. Is the upstream AP some kind of fancy deal or a run of the mill consumer router?
I’ve seen some Cisco APs configured to not allow multiple MAC addresses from the same station. Caused problems when trying to do VMs on my laptop that had the network in bridge mode.
Are you able to put your phone into hotspot, connect to that instead of the upstream AP, and see if it works?