Android Question Sync contact with server

Hi
I need sync user's device contacts with server and contacts are register in database,return their name or only their number that meaning registered in database
But i dont have any idea in mind
I use websocket with b4j and no problem in use it
Only i need best strategy for sync contact
My way is :
get all contacts that have mobile number
Send all it to server
Check numbers in database and return numbers that exist in database
In app i receive their and show number's avatar (each user avatar is base of their phone number)

Regards