The three pages appear to offer different information.
"Software Collections" provides a synopsis of the category and offers a generalized instruction for adding new collections. The other two pages describe different collections for a single module, PHP.
"Software Collections:PHP" seems to describe how to change the PHP for the entire system. If I understand this correctly, there is a risk of unwanted behavior in dependent modules.
"PHP Software Collections" provides a server panel to control which of three PHP installations is run for a given iBay, and these other PHP installs run beside the PHP in the SME distro. That strikes me as a very safe approach.