The primary factor is that 120mm is not the actual focal length of the lens in the phone, that will be a considerably smaller focal length that happens to give the same field of view as a 120mm lens on a full frame camera (i.e. the same sensor size as a 35mm film frame). The phone uses a much smaller sensor than this hence the smaller focal length for the same FoV.
Another thing that helps is using a telephoto lens design - including this lets you create a lens noticeably shorter than its focal length.
When the lens would still make an overly wide phone despite all this that’s where the periscope lens design as others have already mentioned comes in.
how is it physically possible to fit a 120mm lens into a phone?
The primary factor is that 120mm is not the actual focal length of the lens in the phone, that will be a considerably smaller focal length that happens to give the same field of view as a 120mm lens on a full frame camera (i.e. the same sensor size as a 35mm film frame). The phone uses a much smaller sensor than this hence the smaller focal length for the same FoV.
Another thing that helps is using a telephoto lens design - including this lets you create a lens noticeably shorter than its focal length.
When the lens would still make an overly wide phone despite all this that’s where the periscope lens design as others have already mentioned comes in.
Like a periscope. It’s actually pretty cool.
Source
I said equivalency, so I don’t think that’s quite literal. That said, it does stick out a bit and is sunken into the phone itself by about a cm.
I’m not really sure how they get the rest of the way.