I have 4.000 contacts in my iPhone 6s and the new one is XS and just transfer true the iCloud 155 contacts why ?

Contacts are tied to email accounts. When you add email accounts to your phone the associated contacts will come with them. After you have enabled your email accounts if you don’t see your contacts open the Contacts app, tap Groups in the upper left corner, and make sure all groups are checked.

The 4000 contacts are on your memory not in iCloud. This is you have not uploaded then to your iCloud.