Yes—up to a point. A thin camera can have a large front lens element, and real cameras have existed with unusually large glass on relatively compact bodies.

The key issue is not just the front element size, but the relationship between aperture and focal length. Lens brightness is described by the f-number: aperture diameter ≈ focal length ÷ f-number. So for a given focal length, making the lens faster requires a larger entrance pupil.

There is a practical optical limit: for conventional refractive lenses, extremely large apertures become very difficult, and a rough rule of thumb is that photographic lenses don’t get much faster than about f/0.5. Around that range, the lens diameter can approach about twice the lens-to-film/sensor distance, though exact limits depend on lens design and materials.

So: yes, a small or thin camera can have a large lens in front, but there are physical and optical limits to how extreme that can be.