How should I ask a coworker for their phone number?

I work with this one occupational therapist on my unit at my facility. We don't get much time for interaction as she's either with patients or in her office with the door closed. She always smiles and says "Hi" to me every time she passes me in the hall. She seems like a very nice person and I think she's cute and I'd like to be able to talk to her more to get to know her. She usually says hello first, even when I'm not looking, but one time recently I said hello to her first and asked her how she was doing and she got super flustered. I was thinking about putting a note on her car saying "Hey, I've seen you around work and think that you're cute and have a great personality and I'd like to be able to talk more," and then put my phone number. Is that a good way to do so or is it too creepy? With my position I only work 3 days a week since I work longer hours where she works 4-5 days a week, so there are times I only see her once a week.

How should I ask a coworker for their phone number?
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