Pet skills macro the same as normal skills, it is for this reason that they never share a name with a skill for the mage/hunter/warlock class.
You can either assign a keybind directly to the slot on your pet actionbar through the keybind interface (or through whatever bartender-like mod you use), or macro then directly using /cast Freeze (I think that's the name?).
Not sure if it's necessary anymore, but it used to be the case that mages/locks would get more damage out of their pets by macroing their pet's casted attack into their main nuke, triggering it during the lag dead space.
Also useful, if you're new to pet macros (?) are the commands
/petpassive
/petdefensive
/petfollow
/petautocasttoggle (spellname)
/petattack [@mouseover,harm,nodead][]