When your iPhone is buried under sheets, left in another room, or out of sight, the obvious thing to do to locate it is to call your iPhone using another phone. However, this may not be helpful if your iPhone is in silent mode, Do Not Disturb, or has an active Focus mode.
In these situations, or if you don’t have a second phone around, you can use your Apple Watch to play a loud alarm sound on your iPhone or trigger its camera LED to blink.