I try to add this function using the following SQL in phpmyadmin/MySQL
DROP FUNCTION IF EXISTS `__myv`;
DELIMITER ;;
CREATE FUNCTION `__myv`(`a` int, `b`
Even if DELIMITER is a console command, phpMyAdmin's import module has accepted it since many years. When opening a database and clicking on SQL, a query entered there is passed to the import module, so it should work (unless you have a very old phpMyAdmin version).
DELIMITER is a Mysql console command, You can't use it in phpmyadmin. To set the delimiter in phpmyadmin, see this other answer