When I see this girl again how do I asked for her phone number?

just a little bit of background for the question. awhile ago a girl come into my job she was buying something for a construction site.

she came in two other times but i did not have the balls to asked her for her number hopefully she comes back a 4th time.

i was told if she comes back i should try to make personal conversation she's on the clock dont want to keep her from her job

how should i go about asking for her number?

i was just going to be nice & asked her
When I see this girl again how do I asked for her phone number?
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