A space will not work in front. I tried that on something else. The database drops the space (looking at it from MSMM).
If formatting to 7 to 9 digits, then a dash and another number, does work, try this for the mask (set to Reg-Ex) [0-9]?[0-9]?[0-9]?[0-9][0-9][0-9][0-9][0-9]-[0-9]
You can also set the mask in the prompt.