Can i purchase iphone from US and use it in india??

You can use it. But no warranty

IMPORTANT RESTRICTION FOR iPHONE, iPAD, APPLE TV AND HOMEPOD SERVICE.

Apple may restrict warranty service for iPhone, iPad, Apple TV and HomePod to the country where Apple or its Authorized Distributors originally sold the device.

Some iPhones may have variations in their cellular radio coverage that depend on the country or region in which they were meant to be sold. A U.S. phone might support a set of frequencies that's wide enough to be useful for traveling abroad. Would the U.S. phone support the set of frequencies in common use in India, as well as a phone meant for sale in India?

The answer to that is probably highly technical, varying with the specific phones you're considering, but it seems like it might be another possible consideration.