I need my phone besides my bed for personal reasons but how do I restrict using it at night?

You don’t. As in, you don’t need your phone beside your bed. Have the phone in another room, you do not need to hear any messages that come through, and if anything is important enough, a phonecall will wake you up. 💪
Doing this and having your alarm set on your phone will also give you a reason to get out of bed when your alarm goes off, so it’s win win.
There’s absolutely no reason you need your phone beside you, you’re sleeping. Your body and mind need the rest, and your phone is only a distraction. Do this, make yourself do it. It will be hard at first, but within a month you’ll wonder why you haven’t always done it.
I hope this helps, and if you take my advice I think you’ll find it’s for the best. 🙂