I'm not sure this is correct - if phar.phar is installed in $(INSTALL_ROOT)$(bindir) why the link would be in $(bindir)?

because $(INSTALL_ROOT) is used to install file in a temporary location, for example when packaging, while $(bindir) is the location in the filesystem when the package is installed: in Slackware case, the vanilla result installing the package built without the patch is

$ ls -la /usr/bin/phar
lrwxrwxrwx 1 root root 35 mag 8 20:50 /usr/bin/phar -> /tmp/package-php//usr/bin/phar.phar

but there's nothing in /tmp/package-php//usr/bin/phar.phar (the link is broken) and the invocation of phar from the command line fails

$ ls -la /tmp/package-php//usr/bin/phar.phar
/bin/ls: cannot access /tmp/package-php//usr/bin/phar.phar: No such file or directory
$ ls -la /usr/bin/phar.phar
-rwxr-xr-x 1 root root 14823 apr 24 20:32 /usr/bin/phar.phar

that's why when the link is created the destination it should point to ought to be the final one in the filesystem.

driven by the curiosity I've checked how others do: fedora people are forced too fixing this manually when they assemble the package (source http://pkgs.fedoraproject.org/cgit/php.git/plain/php.spec)

(cd $RPM_BUILD_ROOT%{_bindir}; ln -sfn phar.phar phar)

and so opensuse (source https://build.opensuse.org/package/view_file/devel:languages:php/php5/php5.spec)

rm %{buildroot}%{_bindir}/phar
%{__ln_s} -f %{_bindir}/phar.phar %{buildroot}%{_bindir}/phar

Perhaps even a simple (relative link are relative to directory of the link)

  $(LN_S) -f phar.phar $(INSTALL_ROOT)$(bindir)/phar

For downstream packaging link to full path is not correct (can cause some issue in chrooted env, another reason why it is recreated in the fedora .spec file).

@Ponce is there a bug report about this ? (required for NEWS)

I think the reason why is recreated in the fedora .spec file it's because it's broken, as I explained above.
I don't like fedora way because having a link phar in /usr/bin without the full path (/usr/bin/phar.phar) can create problems if someone has another binary called phar.phar in another location that comes first in PATH (~/bin/phar.phar or whatever): this other is called first by the symlink in this case.

regarding the bug report I gotta say I haven't checked...

I think this have to be fixed in all branches (5.5+)

I don't like fedora way because having a link phar in /usr/bin without the full path (/usr/bin/phar.phar) can create problems if someone has another binary called phar.phar in another location that comes first in PATH

No.
As said previously, relative link are relative to link directory. If /usr/bin/phar => phar.phar, "phar" will use /usr/bin/phar.phar and no other scripts.

Example, having ~/bin/phar.phar (echo "Damned") and /usr/bin/phar.phar

$ ll /usr/bin/phar
lrwxrwxrwx. 1 root root 9 15 mai   10:07 /usr/bin/phar -> phar.phar
$ phar.phar 
damned
$ phar
No command given, check /usr/bin/phar help

ah, ok, sorry for the noise. :)

do you want me to do another pull request?

@Ponce yes please, and a bug report

ok, hope I have done everything correctly

#1294
https://bugs.php.net/bug.php?id=69680

ok, hope I have done everything correctly

Yes, thanks