.PHONY pattern rule: match pattern with leading slash - makefile

Question

I am trying to simplify a Makefile. In that, I tried to have a pattern rule for removing files:
.PHONY:
rm-%:
rm $*
where % would contain the name of the file (usually the absolute path with a leading slash).
And then I just state that rm-/some/file is a dependency of make uninstall, and expect make to match this pattern rule.
However, it bite me. I did some tests and realized that the problem was that a leading slash did not match that pattern rule:
~/src/test$ cat Makefile
.PHONY:
a-/%:
$(info /$*)
.PHONY:
b-%:
$(info $*)
.PHONY:
foo: a-/as/d
#:
.PHONY:
bar: b-/as/d
#:
~/src/test$ make foo
/as/d
~/src/test$ make bar
make: *** No rule to make target 'b-/as/d', needed by 'bar'. Stop.
~/src/test$
Why do I need to specify that leading slash in the pattern rule (but not other slashes)?
The GNU make documentation says this:
the ‘%’ matches any nonempty substring, while other characters match
only themselves
https://www.gnu.org/software/make/manual/html_node/Pattern-Intro.html#Pattern-Intro
EDIT: Fix some typos about .PHONY:, use a suffix instead of a prefix as suggested in the answers/comments, and test further:
As I initially suspected, .PHONY: is doing something weird:
~/src/test/$ tree a b c d
a
└── a
b
└── b
c
└── c
d
└── d
0 directories, 4 files
~/src/test$ cat Makefile
%-rmdir:
rmdir $(#D)
%-rm:
rm $*
.PHONY: ./a/.-rmdir
./a/.-rmdir: ./a/a-rm
.PHONY: ./b/-rmdir
./b/-rmdir: ./b/b-rm
./c/.-rmdir: ./c/c-rm
./d/-rmdir: ./d/d-rm
.PHONY: foo
foo: ./a/.-rmdir ./b/-rmdir ./c/.-rmdir ./d/-rmdir
$(info foo)
~/src/test$ make foo
rm a/a
rm b/b
rm c/c
rmdir c
rm d/d
rmdir d
foo

Answer 1

You need to examine the section on How Patterns Match where you will find this text:
When the target pattern does not contain a slash (and it usually does
not), directory names in the file names are removed from the file name
before it is compared with the target prefix and suffix.
(and more detail about how this works).

Answer 2

As per documentation and #MadScientist answer, this is how patterns match. But workaround is very simple: replace your prefix rules with suffix rules and this directory mangling will not stand in the way.
Example:
$ cat Makefile
.PHONY: %-clean
%-clean:
$(info $*)
.PHONY: foo
foo: /as/d-clean
#:
.PHONY: bar
bar: ./as/d-clean
#:
Output:
$ make foo
/as/d
$ make bar
as/d
BTW. Please note that .PHONY: requires target name, it does not automagically apply to the target that follows.