command prompt dail string formating Windows OS

How to format parameter passed to the bat file.
I batch file to start an application from command line with %1 parameter.
Say batch file string looks like one below
Mytest.bat
C:\path\myprog.exe %1
I My case %1 is a caller ID passed from another application where I don’t have any control over to change the format of the telephone number supplied to me.
Phone number passed from the source will look like
 xxxxxxxxx for example 18527956430
While the phone number in the data I want it to compare with is written in format below.
xxx/xxx-xxxx 852/795-6430
 I don’t access or (don’t want to change formatting in the target and I don’t have any control   on the source of %1)
I am looking for the way to break down %1 by characters so I can make original xxxxxxxxxx to look like in the target data set.
So it should look logically something like the string below, but a working script.
C:\path\myprog.exe %1(chars 2,3,4)+ ”/” +%1(chars 5,6,7) +”-“ %(chars 8,9,10,11)
I only have access to the bat file syntax and neither source (ShoreTel easy pop see screenshot attached)  of %1, nor target data cannot be changed. Batch file is started by EasyPop program which is passing caller id.

I only modify  the batch file and don’t have access to Easy Pop or the target data source
easypop.jpg