Apple's Universal Control lets you use your Mac's keyboard and mouse with an iPad, but it doesn't support the iPhone…or anything else.
KeyPad lets you use your Mac Keyboard and Trackpad as a bluetooth keyboard and mouse for the iPhone, android phones, Tablets, TVs, Raspberry Pi and I just verified it on the iPhone Duo. You can:
Type on your iPhone using the Mac’s full Keyboard. Control the iPhone using your Mac’s mouse or trackpad. Switch between multiple paired devices at will. Supports Gaming controls, hold up to 6 keys down at a time. Test iOS app keyboard support without getting a dedicated bluetooth keyboard.
Some technical items:
Mouse control needs you to enable Assistive Touch on the iPhone. KeyPad uses bluetooth only, so does not need an apple account or a network connection. The app itself is less than 3MB, no external libraries.
KeyPad reached #11 in the US Mac App Store - Developer Tools category. Highest it has ever been.
Do try it out, let me know what you think.
https://bluetooth-keyboard.com
https://apps.apple.com/app/keypad-bluetooth-keyboard/id14916...