Just be confident and be yourself mate when you phone, from what you have said it seems like she deff likes you so just go for it
be quite upfront and complimentative if you have to be, like
'the other night was great and i cant get you off my mind so i was wondering wanna do it again some time just me and you?'
something along those lines hasnt yet failed for me, shows her that you do like her and makes her feel that bit more special if you say she has been on your mind all day or whatever.
Other than that im not sure what other advise i can give you but i hope this has been useful, please feel free to send any feedback and goodluck man
-Pulse