Users can search GAL in Online mode : http://contact-outlook.itrezzo.com/2014/05/Global-Address-List-iPhone-Search-vs-Sync.html

 

They can add GAL contacts to their personal Contacts Via : http://tomtalks.uk/2017/05/quickly-copy-outlook-exchange-global-address-list-personal-contact-list-phone/ , however this is manual 

 

This will sync Gal to a contacts list : https://www.cirasync.com/sync-gal-outlook-contacts-iphones/