Getting content of all from a single doctype

I want to get mobile number of all the person in a doctype, in a single place (new variable).
Can anyone help me out ?
What I tried so far is{
    args: {
        doctype:"Dummy User",	   
        fieldname: [ "mobile","name1"],
    callback: function(r) {
    //var a=r.message[0]

But its returning the name of persons present in that doctype. What i want is it returns all the mobile number of persons present in that doctype

See below, it’s fields not fieldname

Worked like charm. Thanks