Run your dev server inside a tab within VS Code, simulating a mobile phone.
A select of device types are available, including a user defined device, for which you can define the width and height in settings. You can use the user defined device to simulate landscape mode by flipping your width and height in the settings.
You can change the URL of your dev server in settings.
I sometimes dev applications for mobile devices so created this extension to help me out, hopefully other people find it useful too.