Transferring contacts from iphone to iphone

Contacts are not stored on the phone, they are associated with and imported from email accounts. To “transfer” contacts you just need to subscribe to the same email accounts on both phones or go to Settings/Contacts/Accounts and add the accounts.

I have 11 email accounts on my phone. There are no problems. You should choose your most frequently used email account to hold your contacts, however, and then chose this as the default account in Settings/Contacts. If you have an iCloud account that would be the first choice, as it syncs automatically in real time if you enable iCloud Contacts.