I think there is a progression. You meet someone and enjoy each others company. Eventually when there is mutual efforts to spend time with each other, whether it be talking on the phone or meeting up somewhere a friendship develops. Sharing personal details about yourself and enjoying each others company. I think my closest friends are the ones who are there for me when I go through bad times, put me in a good mood whenever I talk to them, we love to just be with each other doing nothing special, I miss them when we have had a long lapse in time without communication, I have an emotional attachment to them.
Mostly I think there has to be efforts on both sides to develop and maintain the friendship. It’s like dating, you can’t have just one person doing all of the work, all of the calling, all of the planning.