I’m using Local by Flywheel for my local setup and have installed sage starter theme using composer. I have setup everything as said in the installation documentation.
The address of my local setup is : https://theme.local/
The following is the content of my config.json file
Apparently the flywheel setup routes by HTTP host. Just the IP address alone doesn’t match anything, hence the empty HTTP response.
The easiest way would be configuring your local router to resolve to the localhost IP., so the smartphone also uses it.
The smartphone and your workstation are probably in the same network that is managed by a router device, right? So you log into your router device and a new DNS A record that points from theme.local to 192.168.1.103. Then it should work when you visit theme.local with your smartphone. Even better if you can set up a static workstation IP so you don’t have to update it all the time.
So when your router doesn’t support custom DNS records, set up a local DNS router with passthrough (dnsmasq for example) and let the router use it instead.