Formatting Numbers in text file present in different lines

I have a text file where phone numbers with non-numeric characters are present in different lines.I want to remove the non numeric characters in each line and write it into a new file where each group of digit is present in new line.
 
protected void btnCnvert_Click(object sender, EventArgs e)
{
    string myString;
     int i=0;
     if (FileUpload1.PostedFile != null && FileUpload1.PostedFile.FileName != "")
     {
   
        System.Text.Encoding enc = System.Text.Encoding.ASCII;
        myString = enc.GetString(FileUpload1.FileBytes);

        string[] NoArray;

        NoArray = myString.Split(' ');
           
  &nb ...