You really don't. Cellphones are only a recent part of our history. People lived for thousands of years without them, able to still form meaningful connections.
I'm not here to write an editorial about “how cellphones are killing us all” or “how cellphones are fucking over human connection”, as much as I believe both of those things.
I'm not here to morally grandstand about how much less addicted to technology I am, because I'm not by much. Even though I typically leave behind my laptop when going out, I'm still guilty of wasting an amount my free time checking up on websites that I'd already checked earlier on the same day instead of putting work into creating music. Granted, there should be time set aside for consuming content, but I don't think Twitter really counts.
I am here to tell you what I know, and how I live. “Lead by example instead of by sermon”, as someone wise may have said somewhere to somebody.
So my website's domain probably indicates that I'm a musician. All of my recordings are done through my laptop, because laptops are the most convenient devices through which I can pursue this passion of writing and recording music. My laptop also enables me to communicate with people whenever the need strikes. If a member of my family or one of my friends from assorted locations on this continent wants to contact me, they know how, and I'm generally good about giving a quick response. The Internet is a great way to communicate with people whom you don't live near.
My friends who do live near me are fairly easy to reach face-to-face, as one might expect. Being on a college campus presently, it's often the case that I'll be able to meet up with at least one person for lunch and dinner on the weekdays, and if we want to schedule to hang out beyond that, we have the means of figuring that out right then and there. It is true though that I miss out on occasional spontaneous events that are scheduled last minute over group chats, but as would anyone who may be busy at that very moment. When time for planning is allotted, I'm still invited to things and am able to have a good time with cool people, I'm not concerned with this whole “fear of missing out” thing as a result.
It's fairly easy to argue that owning a cellphone may be useful for safety purposes. If I ever got into some hi-jinks, it would certainly be convenient to have a way of reaching law enforcement. I suppose I'm risking something by not owning a phone, as I suppose I'm risking falling every time I take the stairs or risking choking every time I eat food. As long as I surround myself with trustworthy people and/or don't make stupid decisions, it's pretty easy for me to avoid being in an emergency situation. Heck, I've been in college for two months now and I'm still alive!
The bottom line is that a cellphone is not a necessity, as widely adopted as the technology is. It's literally as simple as that. Go ahead and get one if you're so inclined though; I'm only judging you profusely. :)