3CX Contact & Phone Book synchronization

[aslampa]

We are using Fanvil and Grandstream IP phones........We have more than 500 contacts and 200 extensions....When we do search in the phonebook on IP phones, it is noticed that some of the extensions could not found. I think it could be because number of contacts keep on each phone is different. Is there any way in 3CX we can configure only synch Extensions or External contracts to IP phones? so that we can configure IP phones according to those who prefer to synch Extension or External contacts