Let me define terms first. A "Linux phone" is hardware running a genuinely open mobile OS (postmarketOS, PureOS, Sailfish). To "challenge" Android and iOS means capturing meaningful consumer market share, not just existing. The other side will point to open source's power, and they're right that Linux dominates servers and embedded systems. But mobile isn't servers. Consumers need apps, carrier certification, and third party vendor support. Every Linux phone so far has failed on the app ecosystem, and that's a chicken-and-egg problem money alone can't crack quickly. Without mainstream app developers, it stays a hobbyist niche.