I recently bought the excellent Logitech K380 Multi-Device Bluetooth Keyboard to share between my iPad, Work laptop and iPhone. It’s a great little keyboard, light enough to carry around with a decent layout and spacing that suits my typing style well ( your mileage may vary ). There are however times that I need to switch to the on screen iOS keyboard, typing emojis for example, and I recently discovered this quick tip to bring up the iOS keyboard.
All you need to do is double tap on a text field and the on screen keyboard will pop smoothly into view. Once you have completed using it just hit any key on your Bluetooth keyboard and the hardware device will take control again and the on screen keyboard will slide out of the way.