The principle is the same, but the implementation and results are vastly different.

Both are designed to achieve magnification and bring distant subjects closer using a longer focal length.

Camera Lens: A dedicated telephoto camera lens is a physical, high-quality optic with large glass elements. It produces images with superior sharpness, detail, and authentic background blur (bokeh) thanks to a larger image sensor.

Phone Telephoto: There are primarily two types:

Optical Zoom: The phone has a separate, smaller telephoto camera lens with a physically longer focal length. This is a true telephoto, but its capabilities are limited by the phone's thin body, resulting in a shorter maximum focal length and a much smaller sensor.

Hybrid/Digital Zoom: This crops and digitally enlarges the image from the main wide camera sensor. This process significantly degrades image quality and is not comparable to true optical zoom.

Conclusion: A smartphone's telephoto function is excellent for casual snapshots in good light. However, in terms of overall image quality, low-light performance, zoom range, and the ability to create genuine background blur, it cannot match a dedicated telephoto camera lens for a camera system.