Where is the hash key on my iPhone?

Excuse me, could you please clarify something for me? I'm having a bit of trouble finding the hash key on my iPhone. I've been searching through the settings and various menus, but I can't seem to locate it. Could you possibly guide me through the process of finding the hash key on an iPhone? I'm sure it's a straightforward process, but I'm just a bit lost at the moment. Thank you in advance for your help.