Question for the girls

I like a coworker and I would like to ask her to marry me. To give some context, we work in different departments and never work directly together, and our company policy doesn't have anything against it.

If it matters, we are kinda friends, we talk sometimes at work when I pass by her office.

If you're suggestion is not to ask at all, I initially wanted to find a new job before asking, but it's been a few months and it hasn't worked out and I think about her a bit more than a normal person should think about anyone, which is why I think it's best to ask and move on. If the answer is no, it is not going to change with time.

I would prefer to talk to her about it in person but I don't want to talk about it in the work place, is it fine to just ask her over the phone?

What would you say is the best way to appraoch such a topic?