mysql sets the phone field to be unique. After successfully inserting a record, insert a record with the same phone number. The SQL statement will report an error instead of returning an insertion error! what to do

mysql 设置phone字段为唯一 后 插如一条记录成功 再插入一条手机号一样的记录sql语句报错 而不是返回插入错误！怎么办

<code>$User=M('User');
        $result=$User->add($data);
           if($result){
          $da['code']='1';
          $da['message']="注册成功";
          $da['token']=$data['token'];
               echo json_encode($da);
           }else{
          $da['code']='0';
          $da['message']="手机已注册";
          $da['token']="null";
               echo json_encode($da);
           }```</code>