Tap the red End button on the call screen
Press the side button to lock the iPhone and end the call if needed
Use the volume or mute controls only to silence the call, not end it
If the call is on speaker or Bluetooth, tap End on the active call screen
If using FaceTime, tap the red End button to cut the call
If the screen is unresponsive, press the side button once, then tap End when the call screen appears