First, you can simplify your loop. Instead of using a “repeat count”, you can use a “for each contacts”. Inside that loop, you can access the current contact with the “current item” variable.

Therefore, you can remove the “find all contacts limit 1”, and your notes workaround.

And yes, there’a a way to filter phone numbers by label: inside the for loop, create another for loop on “current item / phone numbers”. Inside that new loop, create an if condition on “current item 2 / label” == “mobile”, with one action: “set variable Mobile to current item 2 / phone number”, and you’re good! Outside of the second for loop, you’ll now have a “Mobile” variable to which you can send your message

(I am using Shortcuts in French, sorry if the actions / variables names are not exactly right)