Can an iPhone bought in Greece work in India?

iPhone is sold buy region, so you'd need to check with your carrier. But please be advised that iPhone Warranty is NOT international. If you have any issue with the phone once you're back in India and you need service or replacement, you'll have to go back to Greece with the phone. If by chance the phone is less expensive in Greece, any savings you might get would be gone plus a whole lot more if something goes wrong with the phone.

It's NEVER a good idea to buy your iPhone in a country you don't live and will use it.

Probably. You will not, however, be able to get it serviced, either pair or under warranty, in India.

If you intend to use it in India, buy it in India.