So I just had another client’s site have a problem, most likely from incompatibility between a plugin they needed and the version of PHP running in their hosting plan. Specifically, the Constant Contact plugin is hasn’t been updated in a while and it still has a (not unreasonable) expectation that you’re running at least PHP 5.5. For reference, PHP 5.5 was released June 20th, 2013, and was only supported up till July of 2016.
So if their hosting plan was such an old legacy plan that they weren’t even running 5.5, that’s…pretty bad customer service.
Currently only about 20% of sites that use PHP are on version 7 (which has been out since 2015, guys!). Version 5.6, the last sub-version of 5, is no longer being supported after December 2018, so get hot guys! Start updating your version of PHP!
If you do go ahead and upgrade your version of PHP and your site crashes (most likely from an incompatibility with the plugins or themes), you can either a) change your theme or plugin or b) theoretically, revert to the earlier version of PHP. I am not 100% convinced this will work but I would like to try to see if I can. Maybe on a local XAMPP stack, update a site and then try to revert it…or maybe pay for a month of hosting just to see if I can toggle back and forth between different versions of PHP. Look for that scintillating adventure soon!