hello my good friend
Normal servo voltages are between 4.8 v and 6 v
anymore than 6 v Dicky and the chances are you fry chippy and that chippy not edible ....

The small motors in a mobile phone - I havent a clue - but I would assume it would be between
1.5 v and 9 v.
To play it safe, try it on 1.5 first and if it looks as though the motor is running slow, increase your voltage at 1.5 intervals by adding another battery.
Hope this helps my good chap.
aye
john
bluebird