If you are using Phoca Gallery version 2.7.5 or later and on your server Suhosin PHP extension is installed, you can run into problems when saving menu link to Phoca Gallery in Menu Manager.
One of the Suhosin security parameter is called suhosin.post.max_vars. Its value is mostly set to 200. But while saving menu link to Phoca Gallery in Menu Manager, more than 200 POST variables are transferred (more than 200 parameters). Unfortunately Suhosin does not retun any error message (this is maybe because of security reasons), the site is redirecting back to main site of Menu Manager and the menu link will be not saved.
It means, if you are not able to save menu link to Phoca Gallery in Menu Manager (Menus - e.g. Main Menu - New - Phoca Gallery - e.g. Phoca Gallery Category List Layout - Save) because the site is redirecting to main site of Menu Manager, try to check your PHP settings:
Joomla! administration - Help - System Info - PHP Information. Try to find 'suhosin' string, try to find the value of suhosin.post.max_vars. If there is such parameter and its value is approximately set to 200, you need to change it in php settings (increase this value e.g. to 250). There are other Suhosin security settings, so if the changing of suhosin.post.max_vars will not help, try to check other Suhosin parameters too.