PHP is the software that runs WordPress. PHP needs to be upgraded, just like WordPress and all your plugins. Like everything else, there is a path of gradual development and this brings more secure and faster code.
The latest versions of PHP are 7.x and yet current usage statistics show 5.4% of WordPress sites are running on PHP 5.2. Support for PHP5.2 ended in 2011. PHP is free so there is no cost for using the latest versions. All Major hosting companies support and offer the latest versions of PHP.
Using an old version is PHP is almost the equivalent of driving around in a 1980 VW Polo when you could upgrade to a 2017 Polo FOR FREE.
What are the potential problems?
You may be using a plugin that will not work with the latest versions of PHP. This is because they could be using code methods no longer supported. if this is the case then you need to ask yourself where you can find a replacement to a plugin that is using standards dropped over 6 years ago. Such plugins are much more likely to be open to hackers. Indeed, some of the largest hack attacks to WordPress in the past few years have been due to people using old versions of Plugins that had upgrades available to fix the issues, but were never updated.
So, there are no really good reasons not to update.
What are the advantages
New versions of PHP are much more secure, and faster. Many sites have seen dramatic improvements in speed. Many of the latest top plugins use new advanced code techniques, that bring faster and more efficient code. They need later versions of PHP to operate.
How do I update?
Contact your web host. Many will have automatic systems. We host this site with SiteGround and within their control panel, we can request a change in the version of PHP to run our sites, and within seconds it is done.
Who is more affected?
The big sites with support contracts and premium hosting plans will have been updated regularly. It is the small sites, in cheap hosting plans that are most affected. There is nobody interested in looking after these sites. No profit to be made. They are also the worst affected when problems start. Too often we hear they get hacked, blame the support they never got and pay another company to create a new site, which, will never be updated either.
Why should WordPress Care?
It may seem that those most affected are going to be the least important websites. However, any of these could grow into something bigger, and we can not ignore them because detractors use their experiences to throw insults and false claims about WordPress.
Has Yoast made a difference?
The Yoast SEO plugin is used by millions of sites around the World. They have added code which ‘NAGS’ sites that have the really oldest versions of PHP to upgrade. Happily, they have been able to report that this method has been very successful. Which just proves that the only thing that is needed is a nudge.
We will be encouraging site owners and developers to use and promote the latest versions of PHP and WordPress for the best results for everyone.