The headphones may be automatically connecting to your iPhone, retaining that connection, and if so, cannot connect to your laptop if it is nearby, as Bluetooth can connect to only one source at a time.
Power your iPhone off as a test, or, if you prefer, simply swipe up the screen from the bottom & select Bluetooth OFF.
Then go to settings on your laptop - Bluetooth - make visible. Press & hold the headphone power button on. Look for the headphones on your laptop Bluetooth list. It should be there now. Click on the WH-CH700N.
Power your iPhone back on, or restore Bluetooth, which you previously turned off.