I’m running Jessie with php version 5.6. My wordpress sites are nagging for an upgrade to 7.0, and ideally to 7.3. Is that possible? I’d rather not upgrade symbiosis: I remember it being fiddly last time round.
The short version is that Bytemark is no longer developing Symbiosis, and it’s starting to have issues with Let’s Encrypt so you won’t be able to automatically get certificate for new domains.
However, I’ve forked Symbiosis as ‘Sympl’, added support for Debian Buster alongside Debian Stretch, and updated the Let’s Encrypt support so it’ll continue to work for the foreseeable future.
Add to that, my new employer is sponsoring development of Sympl as well, and there are some significant improvements in the pipeline.
Your best bet is probably to migrate to Sympl when possible - migration is as easy as possible, and the configuration will just port across.