string regStr1=@"13\d{8}";
string inputStr=rexstr.Text;
string regStr1=@"^13\d{9}$";
string regStr2=@"^\d{3}\d?-\d{8}\d?$";
string regStr3=@"^\d{3}\d?-\d{8}\d?-\d+$";
Regex regex1=new Regex(regStr1,RegexOptions.Compiled);
Regex regex2=new Regex(regStr2,RegexOptions.Compiled);
Regex regex3=new Regex(regStr3,RegexOptions.Compiled);
if(regex1.IsMatch(inputStr)||regex2.IsMatch(inputStr)||regex3.IsMatch(inputStr))
{
return true;
}
else
{
return false;
}