Premium Mobile Devices: Newer flagship phones (like iPhone 12+, Samsung Galaxy S21+, or Pixel 6+) generally have wider-range built-in stereo speakers that can successfully emit frequencies up to 18–20 kHz.
Budget/Older Phones & Tablets: Built-in speakers on older or lower-end devices often physically cannot produce sounds above 12–14 kHz. The software might say it's playing, but the hardware is completely silent.
The External Speaker Secret: For the absolute best results, connect your device to a high-quality external Bluetooth speaker or dedicated PA system that explicitly lists support for high-frequency audio output.