The view class name in symfony is determined per-module, it means that you need to use a module-level configuration setting via the module.yml configuration file. Say you want to use the myView class to handle your view in the default module of your frontend application, create the file sf_root_dir/apps/frontend/config/module.yml and put the following in it:

default:
  view_class:  my

Symfony will add the View suffix for you. Of course, you have to take care of making this class available to the framework. The sf_root_dir/apps/frontend/lib/myView.class.php file would be a good place for this.

As often with sfConfig, you could have put the module.yml config file in sf_root_dir/config/ to make it global to your whole project.

PS: extending the sfPHPView class could be a good idea to get you started too ;)