The exact source and name of the installed version of PHP is important. I also had this problem and installed php56.x86_64 from a remy safe repo. However, only after I installed php.x86_64 from the remi-php56 repository did everything work (and libphp5.so appeared).
I recommend reviewing the installed version and repo source (installed yum list) and then looking for an alternative to one or the other or both (version / repo source).
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