SELECT * FROM `table` AS t1
LEFT OUTER JOIN `phones` AS t2 ON t1.id=t2.cid
WHERE (t1.passSer LIKE '45%') OR (t2.code LIKE '45%')
LIMIT 15

+----+-------------+-------+------------+-------+---------------+----------+---------+--------------------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref                | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+----------+---------+--------------------+------+----------+-------------+
|  1 | SIMPLE      | t1    | NULL       | index | pass,passSer  | name3    | 767     | NULL               |   15 |   100.00 | NULL        |
|  1 | SIMPLE      | t2    | NULL       | ref   | clientID      | clientID | 3       | table.t1.id |    1 |   100.00 | Using where |
+----+-------------+-------+------------+-------+---------------+----------+---------+--------------------+------+----------+-------------+
2 rows in set, 1 warning (0,01 sec)

Note (Code 1003): /* select#1 */ select `table`.`t1`.`id` AS `id`,`table`.`t1`.`name3` AS `name3` from `table`.`clients` `t1` left join `table`.`phones` `t2` on((`table`.`t2`.`clientID` = `table`.`t1`.`id`)) where ((`table`.`t1`.`passSer` like '45%') or (`table`.`t2`.`code` like '45%')) order by `table`.`t1`.`name3` limit 15

`table`.`t2`.`clientID`

(SELECT `id`,`name3`,passser,passnum FROM `clients` WHERE `passSer` LIKE '45%')
UNION ALL
(SELECT `id`,`name3`,t2.code,t2.num FROM `clients` AS `t1`
JOIN `phones` AS t2 ON t1.`id`=t2.`clientID`
WHERE t2.`code` LIKE '45%') ORDER BY name3 LIMIT 15;

+----+--------------+------------+------------+--------+-------------------+---------+---------+--------------------------+-------+----------+----------------------------------------------+
| id | select_type  | table      | partitions | type   | possible_keys     | key     | key_len | ref                      | rows  | filtered | Extra                                        |
+----+--------------+------------+------------+--------+-------------------+---------+---------+--------------------------+-------+----------+----------------------------------------------+
|  1 | PRIMARY      | clients    | NULL       | index  | pass              | name3   | 767     | NULL                     |    15 |    11.11 | Using where                                  |
|  2 | UNION        | t2         | NULL       | ALL    | code_num,clientID | NULL    | NULL    | NULL                     | 42466 |    11.11 | Using where; Using temporary; Using filesort |
|  2 | UNION        | t1         | NULL       | eq_ref | PRIMARY,id_ki_src | PRIMARY | 3       | db.t2.clientID |     1 |   100.00 | NULL                                         |
| NULL | UNION RESULT | <union1,2> | NULL       | ALL    | NULL              | NULL    | NULL    | NULL                     |  NULL |     NULL | Using temporary                              |
+----+--------------+------------+------------+--------+-------------------+---------+---------+--------------------------+-------+----------+----------------------------------------------+
4 rows in set, 1 warning (0,01 sec)

Note (Code 1003): (/* select#1 */ select `db`.`clients`.`id` AS `id`,`db`.`clients`.`name3` AS `name3`,`db`.`clients`.`passSer` AS `passser`,`db`.`clients`.`passNum` AS `passnum`
from `db`.`clients` where (`db`.`clients`.`passSer` like '45%')
order by `db`.`clients`.`name3` limit 15)
union (/* select#2 */ select `db`.`t1`.`id` AS `id`,`db`.`t1`.`name3` AS `name3`,`db`.`t2`.`code` AS `code`,`db`.`t2`.`num` AS `num`
from `db`.`clients` `t1`
join `db`.`phones` `t2`
where ((`db`.`t1`.`id` = `db`.`t2`.`clientID`) and (`db`.`t2`.`code` like '45%'))
order by `db`.`t1`.`name3` limit 15)

(SELECT `id`,`name3`,passser,passnum FROM `clients` WHERE `passSer` LIKE '45%' ORDER BY `name3` LIMIT 15)
UNION
(SELECT `id`,`name3`,t2.code,t2.num FROM `clients` AS `t1`
JOIN `phones` AS t2 ON t1.`id`=t2.`clientID`
WHERE t2.`code` LIKE '45%' ORDER BY `name3` LIMIT 15);

CREATE TABLE `phones`(
`userID` SMALLINT UNSIGNED NOT NULL DEFAULT 0,
`clientID` MEDIUMINT UNSIGNED NOT NULL DEFAULT 0,
`code` SMALLINT(3) NOT NULL DEFAULT 0,
`num` MEDIUMINT(7) ZEROFILL UNSIGNED NOT NULL DEFAULT 0,
`cnt` TINYINT NOT NULL DEFAULT 0,                       # порядковый номер кол-ва телефонов у одного клиента
KEY (`userID`),
KEY (`clientID`),
KEY (`cnt`),    # сортировка
UNIQUE `code_num`(`code`,`num`) # для поиска по телефону
)ENGINE=MyISAM DEFAULT CHARSET=utf8 PACK_KEYS=1;

в клиентах тоже самое, ключи на `passSer_passNum` и отдельно по ним + `name3`
там много столбов ~80

в клиентах тоже самое

CREATE TABLE `clients`(
`id` MEDIUMINT UNSIGNED NOT NULL DEFAULT 0,
`userID` SMALLINT UNSIGNED NOT NULL DEFAULT 0,
`name1` VARCHAR(255) NOT NULL DEFAULT '',
`name2` VARCHAR(255) NOT NULL DEFAULT '',
`name3` VARCHAR(255) NOT NULL DEFAULT '',
`passSer` SMALLINT(4) UNSIGNED ZEROFILL NOT NULL DEFAULT 0,
`passNum` MEDIUMINT(6) UNSIGNED ZEROFILL NOT NULL DEFAULT 0,
PRIMARY KEY (`id`),
KEY (`userID`),
KEY (`name3`),
KEY `pass` (`passSer`,`passNum`),
KEY (`passSer`),
KEY (`passNum`)
)ENGINE=MyISAM DEFAULT CHARSET=utf8 PACK_KEYS=1;

SELECT `id`,`name3`,passser,CONCAT(`passSer2`,' ',`passNum`) AS `ASpass`
FROM `clients`
WHERE `passSer2` LIKE '45%' ORDER BY `name3` LIMIT 15;

explain
SELECT id,name3,CONCAT(`passSer2`,' ',`passNum`) AS `ASpass`
FROM `clients`
WHERE passser2 LIKE '4%'
LIMIT 15;

+----+-------------+---------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
| id | select_type | table   | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra                 |
+----+-------------+---------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
|  1 | SIMPLE      | clients | NULL       | range | passser2      | passser2 | 12      | NULL | 3521 |   100.00 | Using index condition |
+----+-------------+---------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+

+----+-------------+---------+------------+------+---------------+------+---------+------+-------+----------+-------------+
| id | select_type | table   | partitions | type | possible_keys | key  | key_len | ref  | rows  | filtered | Extra       |
+----+-------------+---------+------------+------+---------------+------+---------+------+-------+----------+-------------+
|  1 | SIMPLE      | clients | NULL       | ALL  | pass          | NULL | NULL    | NULL | 39390 |    11.11 | Using where |
+----+-------------+---------+------------+------+---------------+------+---------+------+-------+----------+-------------+