SpaceX Starlink Mobile plans have shaken the US wireless market. Shares of major phone companies fell sharply on Friday. The losses wiped out more than $50 billion in market value before midday. Elon Musk wants SpaceX to become a major mobile carrier in the United States. His plan could bring a new rival to firms that serve millions of phone users. Investors reacted with concern as the company revealed more details about its plans. SpaceX announced the…