oh i hadnt seen the other post, thanks for that.
looks like your trying to accomplish a lot, you need to break it down into manageable pieces which you can do and learn from.
first you need to work out what you will use, you could go a number of ways..
immediately id say a web server but that would require internet on both sides and add more complexity..
a better alternative could be to use tkinter for the controls then access through VNC or some remote login, this can be done through wifi.
if your going for a remote login, you need to research vnc server on the pi3 if thats which you have, and for your phone.
once you can establish a remote login then look at building your program.
if your using tkinter, make a small app which you can run on your computer.
at this point it could be worth getting something like JetBrains Pycharm, which is a python environment for writing and running code from(you would need to look into setting up pycharms interpreters (python and your imports) but im sure youll find a youtube video on that)
As well as been a platform to run your code from Pycharm is also like Microsoft word and will point out grammar errors even if you have incorrect indentation and such within your code. i would have had major difficulty had i not found that a few years back when i started learning python.
either way, make a small tkinter app with a slider http://www.python-course.eu/tkinter_sliders.php
once that is running log in with your phone and view the slider.
next look into LED brightness adjustment with PWM, make the circuit and configure the slider to adjust LED brightness, confirm it with your phone.
wire in your mosfet and adjust the PWM accordingly.
then you have an app to control the motors via your phone
if you was to try this and had any issues im sure many on here would be happy to help you out