how to recover my Apple ID password if my iPhone was stolen?

Your password isn't only on your phone, it is on Apple's computer servers. If you phone was stolen then your Apple ID password hasn't necessarily been stolen too, you have simply forgotten it unless you left it someplace for a thief to easily see it such as having written it down on the back of the phone.

Click on this link to read what to do "If you forgot your Apple ID [Account] password" --> https://support.apple.com/HT201487

or go directly to this link --> http://iforgot.apple.com/

Also read about "What to do after [or before] you change your Apple ID email address or password" --> https://support.apple.com/HT204071

Click on this link for general information about what to do "If your iPhone, iPad, or iPod touch is lost or stolen" --> https://support.apple.com/HT201472