A somatic component is used to designate the target of the spell. Concentration is required to remember the incantation required for a particular spell. Lastly, a verbal component is required to actually cast the spell and I assume it also must vary by what type of spell is cast. This is shown in previous TES games through the spell effects Sound and Silence, one of which reduces the spellcaster's ability to concentrate and creating a chance for failure and the other halting all spellcasting altogether by not allowing the verbal portion of the spell to be performed.
This time around, we have the dragon shouts that activate effects verbally as well, even requiring different combinations of words in the Dragon tongue to form the effects. These shouts have been confirmed to be fully voice-acted.
Neverwinter Nights 2 is a game I can personally remember having phrases of magic (though there may be more), but they were more random I think, and hopefully if magic phrases were included in Skyrim they could vary by effect.
Just out of curiosity, how would people respond to having voice acting for spells as well, including different incantations the characters recite for each type of spell?
Discuss the topic if you like, but please keep it civil, this is just a suggestion out of curiosity.