Should I change the title in my passport to Dr. after getting PhD In many places, a title column is asked where I fill Mr. After getting my PhD can I "officially" change it to Dr.? Is this country dependent? I want to know about India, DrUK and US.
PhD is an academic degree. It is actually dependent on person and country whether to use the title "Dr." in passports and other relevant documents.

However, using Mr. would be wise to avoid a confusion between a doctor (MBBS, MD) and a doctorate (PhD). As per UK gov website, it is not advisable [1]

I have never come across anyone using Dr. in legal documents. Moreover, it is not really a necessity to include Dr. in official/legal documents. For example, I still see my supervisor (who is a senior professor with PhD in 1990s) gets official documents with his name titled "Mr.".