Vim's default motionset is pretty robust but lacks an 'argument' motion ie., delete between arguments.
Usage:
di,
v
public function someFunc($arg1, $arg2, $arg3)
v (normal mode)
public function someFunc($arg1,,$arg3)
ci,
v
public function someFunc($arg1, $arg2, $arg3)
v (insert mode)
public function someFunc($arg1,,$arg3)