You want to put your number in her phone, have her call you or text yourself. Got a lay a few days ago where I put my number in her phone but forgot to have her text me then and there.
Which could’ve lost me the lay if she got scared about texting me first.
It doesn’t really matter how you go about it but generally you should be the one reaching out first afterwards, so you want to have her # regardless of how you go about exchanging.