If you decide to add an extra added value to your résumé, you should look into PHP certifications. Many companies appreciate certifications since they can prove you know more but these are still not the guarantee the knowledge can be taken for granted.
For PHP specific field there is currently the following official PHP certification available:
There are also PHP frameworks specific certifications available for different frameworks and libraries from their official vendors:
Certifications can be taken online and quite a lot of preparation is required for them. In case you decide to take any of the certification exams, make sure you prepare well.