Why do you need to run pecl manually, and why do you think you need the php5 port to do so -- why is the php55 port insufficient for that? If there is a php module you need that does not have a port in MacPorts, please file a port request ticket so that we can add it to MacPorts.
"port contents php55" should not list php-config.1.gz. It should list php-config55.1.gz. Please verify. php5 should not conflict with php55, and does not on my system.
MacPorts says php-config.1.gz already exists and does not belong to a registered port. You're the only one who can explain why that might be so. You can force the activation of php5 if you like, but if you have rogue php5 files on your system already, who knows how many other rogue files you have.
Note that php5 is the "old" MacPorts php world from years ago and is deprecated and will eventually be removed. php53, php54, php55, php56 is the "new" php world which you should be using instead.