Smartphone lenses are often marketed in terms of "optical zoom"[1] relative to the phone's main camera. For example, 120mm is usually referred to as "5× optical zoom", because the main camera's focal length is commonly around 24mm. However, only a few smartphones, such as the Sony Xperia 1 IV and V, include a true zoom lens that offers continuous optical zoom, whereas nearly all smartphones feature a collection of prime lenses interpolated by digital zoom.
Note that this is not a list of the "best" smartphone telephoto lenses, since there are many factors that affect image quality. For example, the Samsung Galaxy S22 Ultra's telephoto lens outperforms the S21 Ultra's, due to hardware and software improvements despite the S22 Ultra's smaller sensor size and shorter focal length.[2]
Another factor is that, within a fixed space, higher focal lengths further constrain the size of the image sensor. Inversely, some manufacturers have recently been able to improve image quality by switching to a lens with a slightly shorter focal length but a much larger sensor.[3] For example, the Vivo X90 Pro+'s 90mm lens still has a 60% larger effective sensor area when digitally cropped to match the field of view of the X80 Pro's 125mm lens.[a]
As such, the following list excludes lenses using sensors smaller than 1/3.5″, which seems to be a lower bound for acceptable image quality (for comparison, most compact travel zoom cameras use 1/2.3″ sensors, which are over twice[b] as large).
