It depends on the phones at both ends as all microphones and speakers have different frequency responses. If either phone has a low quality mic or speaker (one with poor response at the frequencies involved) then your voice will be different.
Bear in mind that small speakers cannot handle bass very well due to physics, cheap speakers cannot handle bass without serious crackling (if they can handle it at all) due to being utter crap. Without the lower frequencies reproduced accurately, things sound higher. This is as true of phones as it is of stereos. many phones these days are also meant to be music/movie players so the sound on them is better than an old Ma Bell wall-phone, but still not as good as decent stereo equipment, so things sound better but still not as good as actually being there.
Also bear on mind that the human voice isn’t just one frequency but a combination of them. A rather blatant example is the voice of Popeye, which was accomplished by Tibetan throat singing and talking in a two-note chord. Not all audio equipment can handle that in it’s full glory, especially not a cheap phone.
My voice tends to sound “flat” and a bit nasally with poor enunciation whenever a microphone is involved unless I drop down a couple of pitches.