Can I pay earlier than 2 years the whole amount for my iPhone?

Yes. With Apple Card you can pay your balance early with no charge.

If using a a 3rd party credit card, then contact the card issuer directly for the installment plan terms. Some plans may not be allowed to be terminated early without an extra charge.

See here: link-> How to apply for Apple Card - Apple Support

Do note you must be a U.S. Citizen or Legal Resident with a U.S. address to apply for an Apple Card.

And also note that with an Apple Card you can pay over 1 year with no interest, but not 2 years. There may be 2 year plans from other card issuers.