Download connection

First we need to download the connection on your computer (that has FSX) which will be the interface to your mobile phone.

Follow steps

Follow the steps to install the program on your computer

Steam version

If you are using the Steam version of FSX ensure you click yes

SimConnect

After the program installs you might need to manually start the simConnect.

Simply locate the program on your computer (you defined this during installation)
-> And click SimConnect.exe

Start up

Now we need to start up FltPlan GPS on your computer
-> Type 'flt' in the start menu and you will see the application
-> Click to open

Firewall

You might get a message that the program cannot connect because of your firewall.
-> Click yes and with Admin rights accept the popup

Ready to go

You can now run FSX and you are ready to 'connect'
-> On the FltPlan GPS program that opened click 'connect'

Which device

In my case I use 'android' to connect so I will say 'no' to this question

Phone - setup

Now switch to your mobile phone and open FltPlan go
-> Click menu
-> Click External

Devices

Tap at the top 'Devices'
-> Scroll down to 'Simulators'
-> Tap FSX

Confirm connection

To confirm you are connected ensure
-> Simulator enabled is displayed FSX
-> Compare the time on 'last update' to your clock on your computer
-> Ensure the GPS data is being displayed which is where your airplane is located in FSX

Map

You can now switch to MAP view (menu)
-> And you should see your airplane located where it is located in FSX
-> In my case it is my FBO which I fly from in real life and FSX

You should setup the view similar how you would fly in real life
-> ensure you use sectionals for OFFLINE (do not use online as in real life if you lose data connection you will not have a view)