The best is always through face to face.
Do it thru phone, and you will have to guess and second guess
yourself, and her, because you cannot see her expression.
When it comes to guts, remember this simple rule.
If you tell her, there may be a chance you might get
accepted. Not tell her, and you will never be
accepted.
Maybe you could start with telling her why you like her, and well,
skim a bit on the mushy parts "I like you ever since i saw you etcs
etcs", and the best way is to tell her that you feel that she makes
a very good friend and wonder if it is possible if both of you can
be more than friends.