No international relations expert, afaik, would say India is in the US sphere of influence; the US specifically says India is not (in what I've seen). India is

No international relations expert, afaik, would say India is in the US sphere of influence; the US specifically says India is not (in what I've seen). India is an independent power that is growing its relationship with the US. It also has relationships with Russia and with others. China happens to be an adversary, which strengthens the US relationship for now. India is nearly unassailable. Nobody can really conquer a country of 1 billion people anyway, economically they have the size (and therefore power) to be independent-minded, and geographically there is no neighbor that is now a serious threat: China can bicker and skirmish but would have to cross the Himalayas to fight a war, which is impossible. Pakistan has nuclear weapons, but those are useless other than to deter an existential attack by India - using them would be suicide. Bangladesh lacks economic, political, and military power. Others are too small. India doesn't need to be in the US 'sphere' and serve US interests.