Using API for SMS Distributions issue with Mailing List

Hello, I am using this API exactly as written but when I use it the resulting distribution comes out like this:
There was 1 contact with a phone number in the mailing list which mailingID I listed in the API, yet it didn't seem to be recognized.
Right now we have phone numbers listed in "Embedded Column A" which is easy enough to pick and choose using a distribution created through the UI, but because we want to schedule many distributions we wish to use API. Has anyone else experienced this issue with getting the API to recognize where the phone numbers (with extension number) are listed within the mailing list? Thanks!