PPSSPP Gold has everything that the free version also has:
PPSSPP Gold also:
PPSSPP Gold is currently available for Android, Windows and macOS.
It is not currently available for Linux or iOS.
More platforms are planned to be added in the future, but as these are by far the most popular two, they got done first.
Whether you own PPSSPP Gold for one of those platforms or not, feel free to use the free version on any platforms you have, as much as you want.
A: The payment provider uses the phone number in its algorithms to prevent credit card fraud. It is not actually used - you will not get calls from anyone.