Pre-installed PHP builds don’t have fpm enabled, so the only option for those installations is to use phpbrew to add the fpm, which recompiles the PHP (slow) but also runs some upgrades for irrelevant php versions (very slow!) and takes like 4 minutes to complee. So it’s a hard no-go.
In my case, I opted in to using the default PHP 7.2 installed on the Ubuntu 18 where adding fpm and other extensions takes way less time. However, it would be a lot better to just have fpm already there in PHP installations that are already provided by semaphoreci/phpbrew. For example, if our systems were using PHP 7.3 then on Ubuntu 18 I’d have no other options except to install/compile it from scratch.