mysql index on varchar and date field for improve query speed of select and insert query
MyISAM and Many insert queries ? 

I definitely recommend to use InnoDB instead of MyISAM. (Don't forget to create backup before change storage)

ALTER TABLE gsm_smslog220717 ENGINE = InnoDB;


If most of your queries for gsm_smslog220717 table like that, you can create composite index for speed up Select query.

ALTER TABLE `gsm_smslog220717` ADD INDEX `affiliateid` (`affiliateid`, `subdt`, `status`);