How to set up a development environment for mobile apps?

I want to build a simple web app to hone my skills with nodejs and other languages.

Basically I already have the basics of the website ready and I uploaded them on a live server using Heroku.

Problem is I want to make changes to the app, but I don't want constantly push any changes to the online website so that I could see the changes on my smartphone.

Therefore, my question is how do I set up a development environment for my mobile app? How to test the app without constantly uploading changes to the live version (I do this via git, so I simply commit and push all changes to the master branch on the live website).

I've tried using the Chrome developer tools by switching it to Mobile view, but after seeing that my app looks a lot differently on my actual smartphone than on the Mobile view on Chrome DevTools I feel very discouraged from using it again.

How do you do it and what are you advise for a noobie? :D