Comment by gaigalas

Those are quite good:

https://launchpad.net/~ondrej/+archive/ubuntu/php

Anyway, whatever you write in an earlier PHP version is likely to work on future versions. PHP has remarkable BC.

If you're just experimenting, might as well start in the browser:

https://alganet.github.io/phasm/

Not all extensions available there, but it has the essentials.