That's not how it is said in English. No native English speaker calls any finger the big finger. What is the big finger? The thumb. Or are you saying it's the middle finger? From what I've learned, अँगूठा is thumb.
The finger pictured in this link is a thumb: https://upload.wikimedia.org/wikipedia/commons/e/ee/Thumbup.jpg
Also, feet don't have fingers. Feet have toes. We do have what we call in English the big toe, but we do not have a big finger.