The best option is to attach the phone to a telescope. E.g. Jupiter with a phone and a 10" Dobsonian.

A 10" Dobsonian isn't small, you're attaching the phone to the scope rather than the other way around.

Size illustration of 8" and 12" Dobsonians vs. a 180 cm (5 feet 11") adult. Adapted from astroshop.eu.

The issue is that the angular resolution of a lens, the smallest feature (in arc seconds) the lens can resolve, scales with the aperture diameter. IMO, anything small enough for a phone attachment isn't going to give enough resolution to be worth the trouble. At best you'll get Jupiter as a bright dot and the Galilean moons as fainter dots.

A 'superzoom' bridge camera like the Nikon P900 can do better. At 357mm f/6.5 (2000mm 'equivalent' focal length) that's a 55mm (or 2") aperture, it's a start.

But honestly, you're better off with a telescope. If a Dobsonian is too big, something like a 5" Mak-Cass is fairly portable and can give better planetary pictures at less cost than a superzoom. You'll still need a tripod. The phone can be handheld close to the eyepiece, or you can use a phone adapter (example).

The best planetary pictures are from stacking a large number of individual frames. Look into stacking and editing when you're ready.