"I like you."
Not really, unless you want to emphasize 'ciebie' (e.g. "Lubię ciebie a nie jego" - "I like YOU and not HIM"). Most of the time you'd say "Lubię cię".
It said another accepted phrase was 'Lubię was' .... was was not even in the selection of words to choose from.
Technically yes, although firstly, of course it means "I like you" as in "I think you're attractive" (so possibly even "I have a crush on you"), and secondly "Podobasz mi się" would feel more natural. But added.