You might have a case for your phone, but it has a cut-out for the lens or lenses so the case doesn't distort the image. In theory, this leaves the lenses vulnerable to damage, but in practice, smartphone camera lenses are extremely tough and practically impossible to seriously scratch. Of course, if you're worried, you can carry your phone in a pouch inside your bag or pocket — or at least make sure to keep it separate from keys and other objects that might scratch it. When cleaning your lenses, use a soft microfiber cloth.