As oh-my-zsh is more of an extended zsh-configuration, it should be sufficient to just tell PHPStorm to use zsh
as Shell. This can be done in the Settings dialog (Menu File->Settings) under section Project Settings->Terminal. Just change Shell Path to the path of zsh
(can be found out with type zsh
in a terminal).
To affect every (new) project you may have to repeat this in File->Default Settigs