Yes, that was incorrect, they are at 780KM orbit, I was thinking Inmarsat who use GEO.
Phased Array does help in improving signal strength(and bandwidth) by focusing on the orbital plane only, however I thought since Iridium uses L-Band(1-2GHz) and SpaceX uses Ku-Band(12-14Ghz), there is additional dish size required anyway and also rain fade issues meant higher strength is required in Ku to operate well.
