Well, there are few options available to try, although I haven't bother doing so yet so I cannot be sure if they will work. On the AAD side of things, you can toggle the "UsersPermissionToReadOtherUsersEnabled" setting, which will restrict users (regular and guest) from viewing other user's details. That's for AAD though, for Exchange/Skype/Teams and every other app that leverages the GAL, you can instead try GAL segmentation, splitting the GAL between regular users and Guests. The steps are explained here: https://technet.microsoft.com/en-us/library/hh529948(v=exchg.150).aspx
Yeah, Vasil, that option is actually huge thou IMO cause if that is on anyone can log into portal.azure.com and view your entire AD Directory lol..... found this out awhile back and was like woah this isn't good. Wish I had known about it when setting up 365 I would have turned it off originally.