I believe the plan is for phased arrays, at both ends, at substantially lower prices than are currently commercially available.
Since SpaceX has already built the "first batch" of satellites (delivered to launch site as of a few days ago), one has to imagine they've largely solved the manufacturing problem and reduced the cost from 250k per antenna.
IIRC, OneWeb's initial plan was to use phased arrays as well, but it proved too expensive and they switched to mechanically steered antennas (at least for first gen).
Phased array is definitely the way to go if you can get cost down. No moving parts means fewer hardware/mechanical failures and less noise
I can easily imagine economies of scale in MMICs (Monolithic Microwave Integrated Circuits) bringing the price down enough to make phased arrays affordable. I sincerely hope it happens.
Since SpaceX has already built the "first batch" of satellites (delivered to launch site as of a few days ago), one has to imagine they've largely solved the manufacturing problem and reduced the cost from 250k per antenna.