Please try out phpcomplete.vim with these test files.

foo.php

<?php

class FooClass {
  public function findme($a, $b = 'foo') {
  }
  public function findme_too($a, $b = 'foo') {
  }
}

Instructions.md

1. Save the gist files to a directory

2. Open vim from that directory

3. :echo tagfiles() should print ['tags'], so we can confirm tags found, the file was generated with ctags -R .

4. Open test.php with :e test.php

5. Hit <c-x><c-o> at the marked place (at the end of line 4)

6. In the completion popup you should see:

    findme    ( f $a, $b = 'foo'
    findme_too( f $a, $b = 'foo'
   

This was tested with https://github.com/shawncplus/phpcomplete.vim/tree/6f093362b11b6e92c0f51075148b93a42859e69f commit.

tags

!_TAG_FILE_FORMAT	2	/extended format; --format=1 will not append ;" to lines/
!_TAG_FILE_SORTED	1	/0=unsorted, 1=sorted, 2=foldcase/
!_TAG_PROGRAM_AUTHOR	Darren Hiebert	/[email protected]/
!_TAG_PROGRAM_NAME	Exuberant Ctags	//
!_TAG_PROGRAM_URL	http://ctags.sourceforge.net	/official site/
!_TAG_PROGRAM_VERSION	5.8	//
FooClass	foo.php	/^class FooClass {$/;"	c
b	foo.php	/^	public function findme($a, $b = 'foo') {$/;"	v
b	foo.php	/^	public function findme_too($a, $b = 'foo') {$/;"	v
f	test.php	/^$f = new FooClass;$/;"	v
findme	foo.php	/^	public function findme($a, $b = 'foo') {$/;"	f
findme_too	foo.php	/^	public function findme_too($a, $b = 'foo') {$/;"	f

test.php

<?php

$f = new FooClass;
$f->fi // <-- hit <c-x><c-o> here