Installing PHP in my home directory

This is all simply:

INSTALL_ROOT=/ DESTDIR=/ make install

I think this because of this, but I am probably wrong:

You use both $PWD/configure --prefix= and the the INSTALL_ROOTvariable with make. Those two options are mutually exclusive.
When you use --prefix, you ask to add a path before each path of files to be installed in the make files. Then you use INSTALL_ROOT variable.

Configure create static make rules; so make couldn't have a way to make some difference:
It add the path you specified with configure a second time.

In order to install php in your home directory (Example: If you don't have root access but need a php executable), run the following commands in your php download folder:

$ ./configure --prefix=/my/path/$ make install

As @Michael Tsang stated, you do not need to specify your install folder a second time as that will lead to the install creating the duplicate folder hierarchy in your install destination. I would also recommend compiling php with the --with-openssl if you're going to be working on a remote server, or using composer for example (simply add the flag to the end of the first command).

Just use

make install

since you have already configured it to be installed in your home. (Better to try it out on a non-root account first)