If you logged into the same iCloud on the new phone as you were signed in on the old phone, and turned on Contacts in iCloud on the new phone, then the contacts should be there. If they are not, then it would mean that some of your contacts are in a different account. Do you have the same email accounts on the iPad as you did on the old iPhone? If so, on the iPad, go to Contacts, check the upper left corner and see if it shows All Groups, or All Contacts. Tap on that, and you will see what other account is listed. You can also check this by going to Settings>Passwords & Accounts. Then look at the account list there and see if any of the accounts besides iCloud have Contacts listed. Then we can work from there.