How to share laptop //localhost with cell phone users using router

I assume you have a router with one WAN port, several LAN ports and WiFi capability. And there is no need to connect to this app from Internet.

You just connect your laptop to any LAN ports, configure DHCP server inside your Netgear router (otherwise you'll have to correctly assign ip addresses from the same subnet for your laptop and your phone). This way your router will be working as a switch bridging your devices in the same network segment, and you'll have connectivity from your phone to your laptop.

Also be sure that your app binds to the laptop's ip address like 192.168... (whichever is configured) and not to 127.0.0.1 (which is the "synonym" of the localhost)

UPD

Check the Windows Firewall, maybe you disabled net access for python when you first run your script binding to 192.168.1.2.