Rather than cleaning up phone numbers just for hashing, we should strip all non-numeric numbers earlier in the process. The nexmo provider requires all-numeric numbers: https://docs.nexmo.com/index.php/verify/verify
Also to assist US phone owners (since we're not used to international phone formats), if number is 10 digits, prepend a '1' automatically.
Closed #787.
ib/7881
Might want to review together with #10288