There's only a few thousand satellites up in orbit right now. Maybe 4000-5000? Half of them are on the other side of the planet at any given time... The service is already strained in a lot of areas. It's not gonna be easy to give bandwidth to another few million phones.
Not just half, but most of them will be below the horizon at any point in time – their orbits are pretty low.
But since mobile phones don't really have directional antennas anyway (unlike Starlink terminals), having more than one satellite in sight above the horizon doesn't really help with capacity anyway. (You need steerable beams on both sides to make use of spatial multiplexing.)
