How to use Shortcuts on my iPhone to call in to conferences?
I did something similar that works for me.  In my case, there's an optional attendee ID as well.  The conference number I'm showing here is 1-555-555-5555


Ask "Meeting access code" (Input type = Number)
Set variable {ConfNum} to {Provided Input}
Ask Attendee ID (Input type = Number, default = 0)
If Provided Input is 0
Text 1555-555-5555,,{ConfNum}#,#
Otherwise
Text 1555-555-5555,,{ConfNum}#,{Provided Input}#
End If
Call {If Result}


Also note that if you use a semicolon (;) instead of a comma (,) for the pause, it will wait until you press a button to dial the remaining string.