@Diana1979
Here are some tips for you if the Tether APP fails to manage device remotely:
1. Make sure the device has internet access.
2. Try connecting your phone to other networks for a comparison, or using celluar data. If other network works, the issue might be with your phone's Internet.
3. Connect to the Wi-Fi network of your Router, go to the Tether APP > Tools > TP-Link ID, unbind your TP-Link ID (account) and rebind it.
4. Modify the DNS Server of the Router. Please go to the web management interface of the Router, go to Advanced > Network > Internet > Advanced Settings > change the DNS server to 8.8.8.8 and 1.1.1.1.
In addition, what is the firmware version of your Archer AX73 V2? please make sure it is the latest version.