In PowerShell ISE, there are little-known built-in debugging features. Provided you have saved your script to a file, you can press F9 to set breakpoints, press F5 to run your script and then have it halt at any breakpoint it hits. Press F11 to step from there, or press F5 to continue the script until it hits another breakpoint or is done.
Check the Debug menu for all debugging options. And note that debugging is not available for scripts that haven't yet been saved to a file.
