It seems to me that priority is not a property of a number type if priority is determined based on the priorities of the other number types, so I think the best approach would be to place the number types in a List.
In other words, you have a List of Lists. The outer List determines the priority of the numbers contained within while the inner List contains the numbers themselves.
Suppose the position 0 in your outer list corresponds to priority A1, position 1 corresponds to priority A2, and position 2 corresponds to priority A3. If you add more priorities later, you can add more, but suffice to say that the number of priorities corresponds to the number of possible number types.
Suppose the user wishes to change the priority of those of A1 to A3. Well according to our List, we'd simply need to remove the first list of numbers and append it to the end. The second item in the list now is the first and the third is now the second. The priority of each number therefore is determined by its position in the list, so you know the priority of a number based on which list you retrieved it from.
I hope that's clear. If not, let me know and I'll try to clarify in my answer.