Which are right: "I lost one of my friend’s phone number" Or "I lost one of my friends’ phone number" [closed]

I believe the teacher is incorrect. There are possibly two interpretations of what the author is speaking of:

  1. they had a friend who had several phone numbers, one of which they lost
  2. they have several friends, and lost the phone number for one of them

The clue to the correct interpretation is that phone number is singular rather than plural, indicating the object of the preposition is 'friends' and not 'number'.

Since it is a reference to one of many friends, then it should be the plural possessive form: friends'