In the days leading up to Apple Inc's (NASDAQ:AAPL) highly-anticipated earnings report, a lesser-known stock sent a warning signal to investors regarding the iPhone maker.

Qorvo Inc (NASDAQ:QRVO), which provides parts for smartphones, reported lower-than-expected as part of its earnings report, raising concerns about Apple's iPhone sales.

What Does Qorvo Do? Qorvo is a key supplier for Apple, providing parts for iPhones, iPads and Apple Watches. Apple buys wireless chips, antenna equipment and ultra-wideband technology from Qorvo. A significant portion of Qorvo's revenue comes from its partnership with Apple.

Qorvo...